View source for Ancient Roman units of measurement

{{Short description|System of measurement used in Ancient Rome}}{{Use dmy dates|date=July 2020}}
[[File:Modio de Ponte Puñide (M.A.N. 1930-16-1) 01.jpg|thumb|Bronze ''modius'' measure (4th century AD) with inscription acknowledging Imperial regulation of weights and measures]]

The '''units of measurement of [[ancient Rome]]''' were generally consistent and well documented.

==Length==
[[File:Roman milestone St Margarethen Austria 201 aC.jpg|thumb|Roman milestone in modern Austria (AD 201), indicating a distance of 28 Roman miles (~41&nbsp;km) to [[Teurnia]]]]
The basic unit of Roman linear measurement was the '''''pes''''' (plural: ''pedes'') or '''Roman foot'''. Investigation of its relation to the [[English units#Length|English<!--not imperial--> foot]] goes back at least to 1647, when [[John Greaves]] published his ''Discourse on the Romane foot''. Greaves visited Rome in 1639, and measured, among other things, the foot measure on the tomb of Titus Statilius Aper, that on the statue of Cossutius formerly in the gardens of [[Angelo Colocci]], the [[congius]] of [[Vespasian]] previously measured by [[Juan Bautista Villalpando|Villalpandus]], a number of brass measuring-rods found in the ruins of Rome, the paving-stones of the [[Pantheon, Rome|Pantheon]] and many other ancient Roman buildings, and the distance between the milestones on the [[Appian Way]]. He concluded that the Cossutian foot was the "true" Roman foot, and reported these values compared to the iron standard of the English foot in the [[Guildhall]] in London<ref name=greaves/>
{| class="wikitable" style="margin: 1em auto 1em auto"
|+ Values of the ancient Roman foot determined by Greaves in 1639
|-
! Source
! Reported value<br>in English feet
! Metric<br>equivalent
|-
|Foot on the statue of Cossutius
|align="center" |0.967&nbsp;
|align="right" | {{cvt|0.967|ft|mm|disp=out}}
|-
|Foot on the monument of Statilius
|align="center" |0.972&nbsp;
|align="right" | {{cvt|0.972|ft|mm|disp=out}}
|-
|Foot of [[Juan Bautista Villalpando|Villalpandus]], derived from [[Congius#Congius of Vespasian|Congius of Vespasian]]
|align="center" |0.986&nbsp;
|align="right" | {{cvt|0.986|ft|mm|disp=out}}
|-
|}

[[William Smith (lexicographer)|William Smith]] (1851) gives a value of 0.9708 English feet, or about 295.9&nbsp;mm.<ref name=smith/> An accepted modern value is 296&nbsp;mm.<ref name=brit/> That foot is also called the ''pes monetalis'' to distinguish it from the ''pes Drusianus'' (about 333 or 335 mm) sometimes used in some provinces, particularly [[Germania Inferior]].<ref name="Dilke" /><ref name="Duncan-Jones" />

The Roman foot was sub-divided either like the Greek ''[[pous]]'' into 16 ''digiti'' or fingers; or into 12 ''unciae'' or inches. [[Frontinus]] writes in the 1st century AD that the ''digitus'' was used in [[Campania]] and most parts of Italy.<ref name=front/> The principal Roman units of length were:

{| class="wikitable" style="margin: 1em auto 1em auto"
|+Ancient Roman units of length
|-
! Roman unit
! English<br>name
! Equal<br>to
! Metric<br>equivalent
! Imperial<br>equivalent
! Notes
|-
| [[digit (unit)|digitus]]
| [[finger (unit)|finger]]
|align="right" | {{frac|1|16}} pes
|align="right" |18.5&nbsp;mm&nbsp;
|align="right" |0.728&nbsp;in&nbsp;<br>0.0607&nbsp;ft&nbsp;
|
|-
| [[Uncia (unit)|uncia]]<br>pollex
| [[inch]]<br>thumb
|align="right" | {{frac|1|12}} pes
|align="right" |24.6&nbsp;mm&nbsp;
|align="right" | 0.971&nbsp;in&nbsp;<br>0.0809&nbsp;ft&nbsp;
|
|-
| [[Palm (unit)|palmus]] (minor)
| palm
|align="right" | {{frac|1|4}} pes
|align="right" |74&nbsp;mm&nbsp;
|align="right" |0.243&nbsp;ft&nbsp;
|
|-
| [[palmus maior]]
| palm length (<small>{{abbr|lit.|literally}}</small>"greater palm")
|align="right" | {{frac|3|4}} pes
|align="right" |222&nbsp;mm&nbsp;
|align="right" |0.728&nbsp;ft&nbsp;
| in late times
|-
| pes (plural: pedes)
| ([[Roman foot|Roman]]) [[foot (unit)|foot]]
|align="right" | 1 pes
|align="right" |296&nbsp;mm&nbsp;
|align="right" |0.971&nbsp;ft&nbsp;
|sometimes distinguished as the ''pes monetalis''{{efn|The ''pes Drusianus'', 333 or 335 mm, was sometimes used in Roman provinces, particularly [[Germania Inferior]].<ref name="Dilke">{{Cite book |last=Dilke |first=Oswald Ashton Wentworth |title=Mathematics and measurement |date=1987 |publisher=British Museum Publications |isbn=978-0-7141-8067-0 |series=Reading the past |location=London|pages=26–27}}</ref><ref name="Duncan-Jones">{{Cite journal |last=Duncan-Jones |first=R. P. |date=1980 |title=Length-Units in Roman Town Planning: The Pes Monetalis and the Pes Drusianus |url=https://www.jstor.org/stable/525675 |journal=Britannia |volume=11 |pages=127–133 |doi=10.2307/525675|jstor=525675 |url-access=subscription }}</ref>}}
|-
| palmipes
| foot and a palm
|align="right" | {{frac|1|1|4}} pedes
|align="right" |370&nbsp;mm&nbsp;
|align="right" |1.214&nbsp;ft&nbsp;
|
|-
| cubitum
| [[cubit]]
|align="right" | {{frac|1|1|2}} pedes
|align="right" |444&nbsp;mm&nbsp;
|align="right" |1.456&nbsp;ft&nbsp;
|
|-
| [[step (unit)|gradus]]<br>pes sestertius
| [[step (unit)|step]]
|align="right" | {{frac|2|1|2}} pedes
|align="right" |0.74&nbsp;m&nbsp;
|align="right" |2.427&nbsp;ft&nbsp;
|
|-
| passus
| [[Pace (unit)|pace]]
|align="right" | 5 pedes
|align="right" |1.48&nbsp;m&nbsp;
|align="right" |4.854&nbsp;ft&nbsp;
|
|-
| decempeda<br>[[pertica (unit)|pertica]]
| [[Perch (unit)|perch]]
|align="right" | 10 pedes
|align="right" |2.96&nbsp;m&nbsp;
|align="right" |9.708&nbsp;ft&nbsp;
|
|-
| {{vanchor|Actus|text=actus}}
|path, track
|align="right" | 120 pedes
|align="right" |35.5&nbsp;m&nbsp;
|align="right" |116.496&nbsp;ft&nbsp;
|[[24 (number)|24 passus]] or [[12 (number)|12]] decembeda
|-
| [[Stadion (unit)|stadium]]
| stade
|align="right" | 625 pedes
|align="right" |185&nbsp;m&nbsp;
|align="right" |607.14&nbsp;ft&nbsp;
| [[600 (number)|600]] [[Greek feet]]<br /> or 125 passus <br /> or {{frac|8}} mille<ref>Equivalent to the English [[Cable_length|cable]] (600 feet) or [[furlong]] ({{frac|8}} mile)</ref>
|-
| [[mille passus]]<br>mille passuum
| ([[Roman mile|Roman]]) [[mile]]
|align="right" | 5,000 pedes
|align="right" |1.48&nbsp;km&nbsp;
|align="right" |4,854&nbsp;ft&nbsp;<br>0.919&nbsp;[[international mile|mi]]&nbsp;
| 1000 passus or 8 stadia
|-
| leuga<br>leuca
| (Gallic) [[League (unit)|league]]
|align="right" | 7,500 pedes
|align="right" |2.22&nbsp;km&nbsp;
|align="right" |7,281&nbsp;ft&nbsp;<br>1.379&nbsp;[[international mile|mi]]&nbsp;
|
|-
| colspan=6 style= "font-size:smaller" | Except where noted, based on Smith (1851).<ref name=smith/><br>English and metric equivalents are approximate, converted at 1 pes = 0.9708 English feet and 296&nbsp;mm respectively.
|-
|}

Other units include the [[schoenus]] (from the Greek for "[[Juncaceae|rush]] rope") used for the distances in [[Isidore of Charax]]'s ''[[Parthian Stations]]'' (where it had a value around {{convert|5|km|mile|0|abbr=in|disp=or}})<ref>{{cite book|url=https://books.google.com/books?id=DQgmOZlsEWcC|title=Between Rome and Persia: The Middle Euphrates, Mesopotamia and Palmyra Under Roman Control|first=Peter|last=Edwell|year=2007|publisher=Routledge|page=228|isbn=9781134095735}}</ref><ref>{{cite book|url=https://books.google.com/books?id=41-0AwAAQBAJ&pg=PT105|title=Amurath to Amurath: Includes Biography of Gertrude Bell|first1=Gertrude|last1=Bell|author-link1=Gertrude Bell|first2=Fergus|last2=Mason|year=2014|publisher=BookCaps Study Guides|page=105|isbn=9781629172859}}</ref> and in the name of the [[Nubia]]n land of [[Triacontaschoenus]] between the [[First Cataract|First]] and [[Second Cataract]]s on the [[Nile]] (where it had a value closer to {{convert|10.5|km|mile|frac=2|abbr=in|disp=or}}).<ref>{{cite book|url=https://books.google.com/books?id=Or5CKl1ObX4C|title=The Histories|last=Herodotus|year=1998|publisher=OUP Oxford|page=592|isbn=9780191589553}}</ref><ref>{{cite book|url=https://books.google.com/books?id=jjBYQCpfCNkC|title=The Cambridge History of Africa|first=J. D.|last=Fage|year=1979|publisher=Cambridge University Press|page=258|isbn=9780521215923}}</ref>

==Area==

The ordinary units of measurement of area were:
{| class="wikitable" style="margin: 1em auto 1em auto"
|+ Ancient Roman units of area
|-
! Roman unit
! English<br>name
! Equal<br>to
! Metric<br>equivalent
! Imperial<br>equivalent
! Description
|-
| pes quadratus
| square foot
|align="right" | 1 pes qu.
|align="right" | 0.0876&nbsp;m{{sup|2}}&nbsp;
|align="right" | 0.943&nbsp;sq&nbsp;ft&nbsp;
|
|-
| style="max-width:0" | [[scrupulum]] or decempeda quadrata
|
|align="right" | 100 pedes qu.
|align="right" | 8.76&nbsp;m{{sup|2}}&nbsp;
|align="right" | 94.3&nbsp;sq&nbsp;ft&nbsp;
| style="max-width:0" | the square of the standard 10-foot measuring rod
|-
| actus simplex
|
|align="right" | 480 pedes qu.
|align="right" | 42.1&nbsp;m{{sup|2}}&nbsp;
|align="right" | 453&nbsp;sq&nbsp;ft&nbsp;
|4 × 120 pedes<ref name=Millar/>
|-
| uncia
|
|align="right" | 2,400 pedes qu.
|align="right" | 210&nbsp;m{{sup|2}}&nbsp;
|align="right" | 2,260&nbsp;sq&nbsp;ft&nbsp;
|
|-
| clima
|
|align="right" | 3,600 pedes qu.
|align="right" | 315&nbsp;m{{sup|2}}&nbsp;
|align="right" | 3,390&nbsp;sq&nbsp;ft&nbsp;
|60 × 60 pedes<ref name=Millar/>
|-
| actus quadratus or acnua
|
|align="right" | 14,400 pedes qu.
|align="right" | 1,262&nbsp;m{{sup|2}}&nbsp;
|align="right" | 13,600&nbsp;sq&nbsp;ft&nbsp;
|also called ''arpennis'' in [[Gaul]]<ref name=Millar/>
|-
| [[jugerum]]
|
|align="right" | 28,800 pedes qu.
|align="right" | 2,523&nbsp;m{{sup|2}}&nbsp;
|align="right" | 27,200&nbsp;sq&nbsp;ft&nbsp;<br>0.623&nbsp;acres&nbsp;
|
|-
| heredium
|
|align="right" | 2 jugera
|align="right" | 5,047&nbsp;m{{sup|2}}&nbsp;
|align="right" | 54,300&nbsp;sq&nbsp;ft&nbsp;<br>1.248&nbsp;acres&nbsp;
|
|-
| [[Centuria (unit of measure)|centuria]]
|
|align="right" | 200 jugera
|align="right" | 50.5 [[hectare|ha]]&nbsp;
|align="right" | 125&nbsp;acres&nbsp;
|formerly 100 jugera<ref name=Millar/>
|-
| saltus
|
|align="right" | 800 jugera
|align="right" | 201.9&nbsp;ha&nbsp;
|align="right" | 499&nbsp;acres&nbsp;
|
|-
|modius
|
|align="right" | 
|align="right" | 16&nbsp;ha&nbsp;
|align="right" | 40&nbsp;acres&nbsp;
|[[Medieval Latin]], plural modii<ref>{{cite book|last=Davies |first=Wendy|authorlink=Wendy Davies  |title=An Early Welsh Microcosm: Studies in the Llandaff Charters|page=33|publisher=Royal Historical Society |location =London, UK |year=1978|isbn=978-0-901050-33-5}}</ref>
|-
| colspan=6 style= "font-size:smaller" | Except where noted, based on Smith (1851).<ref name=smith/> Metric equivalents are approximate, converted at 1 pes = 296&nbsp;mm.
|-
|}

Other units of area described by [[Columella]] in his ''De Re Rustica'' include the ''porca'' of 180 × 30 Roman feet (about {{convert|473|m2|sqft|abbr=on|disp=or}}) used in [[Hispania Baetica]] and the Gallic ''candetum'' or ''cadetum'' of 100 feet{{clarify|reason=100 square feet or 100 feet square (i.e. 10,000 square feet)?|date=October 2016}} in the city or 150 in the country. Columella also gives uncial divisions of the ''jugerum'', tabulated by the anonymous translator of the 1745 Millar edition as follows:

{| class="wikitable" style="margin: 1em auto 1em auto"
|+Uncial divisions of the ''jugerum''
|-
! Roman<br>unit
! Roman<br>square feet
! Fraction<br>of jugerum
! Metric<br>equivalent
! Imperial<br>equivalent
! Description
|-
| dimidium scrupulum
|align="right" | 50
|align="right" | {{frac|1|576}}
|align="right" | 4.38&nbsp;m{{sup|2}}&nbsp;
|align="right" | 47.1&nbsp;sq&nbsp;ft&nbsp;
|
|-
| scrupulum
|align="right" | 100
|align="right" | {{frac|1|288}}
|align="right" | 8.76&nbsp;m{{sup|2}}&nbsp;
|align="right" | 94.3&nbsp;sq&nbsp;ft&nbsp;
|
|-
| duo scrupula
|align="right" | 200
|align="right" | {{frac|1|144}}
|align="right" | 17.5&nbsp;m{{sup|2}}&nbsp;
|align="right" | 188&nbsp;sq&nbsp;ft&nbsp;
|
|-
| sextula
|align="right" | 400
|align="right" | {{frac|1|72}}
|align="right" | 35.0&nbsp;m{{sup|2}}&nbsp;
|align="right" | 377&nbsp;sq&nbsp;ft&nbsp;
|
|-
| sicilicus
|align="right" | 600
|align="right" | {{frac|1|48}}
|align="right" | 52.6&nbsp;m{{sup|2}}&nbsp;
|align="right" | 566&nbsp;sq&nbsp;ft&nbsp;
|
|-
| semiuncia
|align="right" | 1,200
|align="right" | {{frac|1|24}}
|align="right" | 105&nbsp;m{{sup|2}}&nbsp;
|align="right" | 1,130&nbsp;sq&nbsp;ft&nbsp;
|
|-
| uncia
|align="right" | 2,400
|align="right" | {{frac|1|12}}
|align="right" | 210&nbsp;m{{sup|2}}&nbsp;
|align="right" | 2,260&nbsp;sq&nbsp;ft&nbsp;
|
|-
| sextans
|align="right" | 4,800
|align="right" | {{frac|1|6}}
|align="right" | 421&nbsp;m{{sup|2}}&nbsp;
|align="right" | 4,530&nbsp;sq&nbsp;ft&nbsp;
|
|-
| quadrans
|align="right" | 7,200
|align="right" | {{frac|1|4}}
|align="right" | 631&nbsp;m{{sup|2}}&nbsp;
|align="right" | 6,790&nbsp;sq&nbsp;ft&nbsp;
|
|-
| triens
|align="right" | 9,600
|align="right" | {{frac|1|3}}
|align="right" | 841&nbsp;m{{sup|2}}&nbsp;
|align="right" | 9,050&nbsp;sq&nbsp;ft&nbsp;
|
|-
| quincunx
|align="right" | 12,000
|align="right" | {{frac|5|12}}
|align="right" | 1,051&nbsp;m{{sup|2}}&nbsp;
|align="right" | 11,310&nbsp;sq&nbsp;ft&nbsp;
|
|-
| semis
|align="right" | 14,400
|align="right" | {{frac|1|2}}
|align="right" | 1,262&nbsp;m{{sup|2}}&nbsp;
|align="right" | 15,380&nbsp;sq&nbsp;ft&nbsp;
| = actus quadratus<ref name=smith/>
|-
| septunx
|align="right" | 16,800
|align="right" | {{frac|7|12}}
|align="right" | 1,472&nbsp;m{{sup|2}}&nbsp;
|align="right" | 15,840&nbsp;sq&nbsp;ft&nbsp;
|
|-
| bes
|align="right" | 19,200
|align="right" | {{frac|2|3}}
|align="right" | 1,682&nbsp;m{{sup|2}}&nbsp;
|align="right" | 18,100&nbsp;sq&nbsp;ft&nbsp;
|
|-
| dodrans
|align="right" | 21,600
|align="right" | {{frac|3|4}}
|align="right" | 1,893&nbsp;m{{sup|2}}&nbsp;
|align="right" | 20,380&nbsp;sq&nbsp;ft&nbsp;
|
|-
| dextans
|align="right" | 24,000
|align="right" | {{frac|5|6}}
|align="right" | 2,103&nbsp;m{{sup|2}}&nbsp;
|align="right" | 22,640&nbsp;sq&nbsp;ft&nbsp;
|
|-
| deunx
|align="right" | 26,400
|align="right" | {{frac|11|12}}
|align="right" | 2,313&nbsp;m{{sup|2}}&nbsp;
|align="right" | 24,900&nbsp;sq&nbsp;ft&nbsp;
|
|-
| jugerum
|align="right" | 28,800
|align="right" | 1
|align="right" | 2,523&nbsp;m{{sup|2}}&nbsp;
|align="right" | 27,160&nbsp;sq&nbsp;ft&nbsp;
|
|-
| colspan=6 style= "font-size:smaller" | Except where noted, based on Millar (1745).<ref name=Millar/> Metric equivalents are approximate, converted at 1 pes = 296&nbsp;mm.
|}

==Volume==

Both liquid and dry volume measurements were based on the {{lang|la|sextarius}}. The sextarius was defined as {{frac|48}} of a cubic {{lang|la|pes}} (Roman foot), known as an {{lang|la|[[amphora]] quadrantal}}. Using the value {{convert|296|mm|in|abbr=on}} for the Roman foot, an amphora quadrantal can be computed at approximately {{convert|25.9|L|abbr=on}}, so a sextarius (by the same method) would theoretically measure {{convert|540.3|ml|floz|abbr=on}}, which is about 95% of an [[pint#Imperial pint|imperial pint]] ({{cvt|1.000|imppt|ml|disp=out}}).

Archaeologically, however, the evidence is not as precise. No two surviving vessels measure an identical volume, and scholarly opinion on the actual volume ranges between {{convert|500|and(-)|580|ml|USfloz|abbr=on}}.<ref>{{cite web|url=http://www.masseiana.org/pliny.htm|title=Pliny's Natural History (Introduction to Chapter 6)|author=W.H. Jones|year=1954|access-date=1 June 2014|archive-url=https://web.archive.org/web/20170101063545/http://www.masseiana.org/pliny.htm|archive-date=1 January 2017|url-status=usurped}}</ref><ref name=zupko/>

The core volume units are:
* ''[[amphora quadrantal]]'' (Roman jar) – one cubic ''pes'' (Roman foot)
* ''congius'' – a half-''pes'' cube (thus {{frac|1|8}} ''amphora quadrantal'')
* ''sextarius'' – literally {{frac|1|6}} of a ''congius''

===Liquid measure===
{| class="wikitable"
|+ Ancient Roman liquid measures
|-
! Roman unit
! Equal to
! Metric
! Imperial
! US fluid
|-
|style="padding:0 8px;"| ligula
|style="padding:0 8px; text-align:right;"| {{frac|1|288}} congius
|style="padding:0 8px; text-align:right;"| 11.4 mL
|style="padding:0 8px; text-align:right;"| 0.401 fl oz
|style="padding:0 8px; text-align:right;"| 0.385 fl oz
|-
|style="padding:0 8px;"| cyathus
|style="padding:0 8px; text-align:right;"| {{frac|1|72}} congius
|style="padding:0 8px; text-align:right;"| 45 mL
|style="padding:0 8px; text-align:right;"| 1.58 fl oz
|style="padding:0 8px; text-align:right;"| 1.52 fl oz
|-
|style="padding:0 8px;"| acetabulum
|style="padding:0 8px; text-align:right;"| {{frac|1|48}} congius
|style="padding:0 8px; text-align:right;"| 68 mL
|style="padding:0 8px; text-align:right;"| 2.39 fl oz
|style="padding:0 8px; text-align:right;"| 2.30 fl oz
|-
|style="padding:0 8px;"| quartarius
|style="padding:0 8px; text-align:right;"| {{frac|1|24}} congius
|style="padding:0 8px; text-align:right;"| 136 mL
|style="padding:0 8px; text-align:right;"| 4.79 fl oz
|style="padding:0 8px; text-align:right;"| 4.61 fl oz
|-
|style="padding:0 8px;"| {{linktext|hemina}} or cotyla
|style="padding:0 8px; text-align:right;"| {{frac|1|12}} congius
|style="padding:0 8px; text-align:right;"| 273 mL
|style="padding:0 8px; text-align:right;"| 9.61 fl oz
|style="padding:0 8px; text-align:right;"| 9.23 fl oz
|-
|style="padding:0 8px;"| sextarius
|style="padding:0 8px; text-align:right;"| {{frac|1|6}} congius
|style="padding:0 8px; text-align:right;"| 546 mL
|style="padding:0 8px; text-align:right;"| 19.22 fl oz<br>0.961 pt
|style="padding:0 8px; text-align:right;"| 18.47 fl oz<br>1.153 pt
|-
|style="padding:0 8px;"| congius
|style="padding:0 8px; text-align:right;"| 1 congius
|style="padding:0 8px; text-align:right;"| 3.27 L
|style="padding:0 8px; text-align:right;"| 5.75 pt<br>0.719 gal
|style="padding:0 8px; text-align:right;"| 3.46 qt<br>0.864 gal
|-
|style="padding:0 8px;"| urna
|style="padding:0 8px; text-align:right;"| 4 congii
|style="padding:0 8px; text-align:right;"| 13.1 L
|style="padding:0 8px; text-align:right;"| 2.88 gal
|style="padding:0 8px; text-align:right;"| 3.46 gal
|-
|style="padding:0 8px;"| amphora quadrantal
|style="padding:0 8px; text-align:right;"| 8 congii
|style="padding:0 8px; text-align:right;"| 26.2 L
|style="padding:0 8px; text-align:right;"| 5.76 gal
|style="padding:0 8px; text-align:right;"| 6.92 gal
|-
|style="padding:0 8px;"| culeus
|style="padding:0 8px; text-align:right;"| 160 congii
|style="padding:0 8px; text-align:right;"| 524 L
|style="padding:0 8px; text-align:right;"| 115.3 gal
|style="padding:0 8px; text-align:right;"| 138.4 gal
|-
|colspan=5 style="font-size:smaller;"| Except where noted, based on Smith (1851).<ref name="smith" /><br />Modern equivalents are approximate.
|}

===Dry measure===
{| class="wikitable"
|+ Ancient Roman dry measures
|-
! Roman unit
! Equal to
! Metric
! Imperial
! US dry
|-
|style="padding:0 8px;"| ligula
|style="padding:0 8px; text-align:right;"| {{frac|1|288}} congius
|style="padding:0 8px; text-align:right;"| 11.4 ml
|style="padding:0 8px; text-align:right;"| 0.401 fl oz
|style="padding:0 8px; text-align:right;"| 0.0207 pt
|-
|style="padding:0 8px;"| cyathus
|style="padding:0 8px; text-align:right;"| {{frac|1|72}} congius
|style="padding:0 8px; text-align:right;"| 45 ml
|style="padding:0 8px; text-align:right;"| 1.58 fl oz
|style="padding:0 8px; text-align:right;"| 0.082 pt
|-
|style="padding:0 8px;"| acetabulum
|style="padding:0 8px; text-align:right;"| {{frac|1|48}} congius
|style="padding:0 8px; text-align:right;"| 68 ml
|style="padding:0 8px; text-align:right;"| 2.39 fl oz
|style="padding:0 8px; text-align:right;"| 0.124 pt
|-
|style="padding:0 8px;"| quartarius
|style="padding:0 8px; text-align:right;"| {{frac|1|24}} congius
|style="padding:0 8px; text-align:right;"| 136 ml
|style="padding:0 8px; text-align:right;"| 4.79 fl oz
|style="padding:0 8px; text-align:right;"| 0.247 pt
|-
|style="padding:0 8px;"| hemina or cotyla
|style="padding:0 8px; text-align:right;"| {{frac|1|12}} congius
|style="padding:0 8px; text-align:right;"| 273 ml
|style="padding:0 8px; text-align:right;"| 9.61 fl oz
|style="padding:0 8px; text-align:right;"| 0.496 pt
|-
|style="padding:0 8px;"| sextarius
|style="padding:0 8px; text-align:right;"| {{frac|1|6}} congius
|style="padding:0 8px; text-align:right;"| 546 ml
|style="padding:0 8px; text-align:right;"| 19.22 fl oz<br>0.961 pt
|style="padding:0 8px; text-align:right;"| 0.991 pt
|-
|style="padding:0 8px;"| semimodius
|style="padding:0 8px; text-align:right;"| {{frac|1|1|3}} congii
|style="padding:0 8px; text-align:right;"| 4.36 L
|style="padding:0 8px; text-align:right;"| 0.96 gal
|style="padding:0 8px; text-align:right;"| 0.99 gal
|-
|style="padding:0 8px;"| modius
|style="padding:0 8px; text-align:right;"| {{frac|2|2|3}} congii
|style="padding:0 8px; text-align:right;"| 8.73 L
|style="padding:0 8px; text-align:right;"| 1.92 gal
|style="padding:0 8px; text-align:right;"| 1.98 gal
|-
|style="padding:0 8px;"| modius castrensis
|style="padding:0 8px; text-align:right;"| 4 congii
|style="padding:0 8px; text-align:right;"| 12.93 L<ref>Dominic Rathbone, "Earnings and Costs: Living Standards and the Roman Economy (First to Third Centuries AD), p. 301, in Alan Bowman and Andrew Wilson, ''Quantifying the Roman Economy: Methods and Problems''.</ref>
|style="padding:0 8px; text-align:right;"| 2.84 gal
|style="padding:0 8px; text-align:right;"| 2.94 gal
|-
|colspan=5 style="font-size:smaller;"| Except where noted, based on Smith (1851).<ref name="smith" /><br />Modern equivalents are approximate.
|}

==Weight==
[[File:Roman steelyard weight (probably) (FindID 227547).jpg|thumb|A Roman steelyard weight of one ''dodrans'', i.e. {{frac|3|4}} libra]]
The units of weight or [[mass]] were mostly based on factors of 12. Several of the unit names were also the names of coins during the [[Roman Republic]] and had the same fractional value of a larger base unit: libra for weight and [[as (Roman coin)|as]] for coin. Modern estimates of the libra range from {{convert|322|to|329|g|oz|abbr=on}} with 5076 grains or {{convert|328.9|g|oz|abbr=on}} an accepted figure.<ref name=brit/><ref name=zupko/><ref name=skinner/> The ''as'' was reduced from 12 ounces to 2 after the [[First Punic War]], to 1 during the [[Second Punic War]], and to half an ounce by the 131&nbsp;BC [[Lex Papiria]].<ref name=oedas>{{Citation |title=Oxford English Dictionary |edition=1st |contribution=as, ''n''. |date=1885 |publisher=Oxford University Press |location=Oxford}}.</ref><ref name=dgra1875>{{Citation |title=A Dictionary of Greek and Roman Antiquities|contribution=Tabellariae Leges. |date=1875 |publisher=John Murray |location=London}}.</ref>

The divisions of the libra were:
{| class="wikitable" style="margin: 1em auto 1em auto"
|+Uncial divisions of the libra
|-
! Roman unit
! English<br>name
! Equal<br>to
! Metric<br>equivalent
! Imperial<br>equivalent
! Description
|-
| uncia
| Roman ounce
|align="right" | {{frac|1|12}} libra
|align="right" | 27.4&nbsp;g&nbsp;
|align="right" | 0.967&nbsp;oz&nbsp;
|<small>{{abbr|lit.|literally}}</small>&nbsp;"a twelfth"<ref name=uncia>{{Cite web |title=Charlton T. Lewis, Charles Short, A Latin Dictionary, U , umbrōsus , uncĭa |url=https://www.perseus.tufts.edu/hopper/text?doc=Perseus:text:1999.04.0059:alphabetic+letter=U:entry+group=3:entry=uncia |access-date=2024-08-08 |website=www.perseus.tufts.edu}}</ref>
|-
| sescuncia or sescunx
|
|align="right" | {{frac|1|8}} libra
|align="right" | 41.1&nbsp;g&nbsp;
|align="right" | 1.45&nbsp;oz&nbsp;
|<small>{{abbr|lit.|literally}}</small>&nbsp;"one and one-half twelfths"
|-
| sextans
|
|align="right" | {{frac|1|6}} libra
|align="right" | 54.8&nbsp;g&nbsp;
|align="right" | 1.93&nbsp;oz&nbsp;
|<small>{{abbr|lit.|literally}}</small>&nbsp;"a sixth"
|-
| quadrans<br>teruncius
|
|align="right" | {{frac|1|4}} libra
|align="right" | 82.2&nbsp;g&nbsp;
|align="right" | 2.90&nbsp;oz&nbsp;
|<small>{{abbr|lit.|literally}}</small>&nbsp;"a fourth"<br><small>{{abbr|lit.|literally}}</small>&nbsp;"triple twelfth"
|-
| triens
|
|align="right" | {{frac|1|3}} libra
|align="right" | 109.6&nbsp;g&nbsp;
|align="right" | 3.87&nbsp;oz&nbsp;
|<small>{{abbr|lit.|literally}}</small>&nbsp;"a third"
|-
| quincunx
|
|align="right" | {{frac|5|12}} libra
|align="right" | 137.0&nbsp;g&nbsp;
|align="right" | 4.83&nbsp;oz&nbsp;
|<small>{{abbr|lit.|literally}}</small>&nbsp;"five-twelfths"<ref>{{Citation |title=Oxford English Dictionary, ''3rd ed''. |contribution=quincunx, ''n.'' |date=2007 |publisher=Oxford University Press |location=Oxford}}.</ref>
|-
| semis or semissis
|
|align="right" | {{frac|1|2}} libra
|align="right" | 164.5&nbsp;g&nbsp;
|align="right" | 5.80&nbsp;oz&nbsp;
|<small>{{abbr|lit.|literally}}</small>&nbsp;"a half"
|-
| septunx
|
|align="right" | {{frac|7|12}} libra
|align="right" | 191.9&nbsp;g&nbsp;
|align="right" | 6.77&nbsp;oz&nbsp;
|<small>{{abbr|lit.|literally}}</small>&nbsp;"seven-twelfths"
|-
|bes or bessis
|
|align="right" | {{frac|2|3}} libra
|align="right" | 219.3&nbsp;g&nbsp;
|align="right" | 7.74&nbsp;oz&nbsp;
|<small>{{abbr|lit.|literally}}</small>&nbsp;"two [parts] of an ''as''"
|-
| dodrans
|
|align="right" | {{frac|3|4}} libra
|align="right" | 246.7&nbsp;g&nbsp;
|align="right" | 8.70&nbsp;oz&nbsp;
|<small>{{abbr|lit.|literally}}</small>&nbsp;"less a fourth"
|-
| dextans
|
|align="right" | {{frac|5|6}} libra
|align="right" | 274.1&nbsp;g&nbsp;
|align="right" | 9.67&nbsp;oz&nbsp;
|<small>{{abbr|lit.|literally}}</small>&nbsp;"less a sixth"
|-
| deunx
|
|align="right" | {{frac|11|12}} libra
|align="right" | 301.5&nbsp;g&nbsp;
|align="right" | 10.64&nbsp;oz&nbsp;
|<small>{{abbr|lit.|literally}}</small>&nbsp;"less a twelfth"
|-
| libra
| Roman pound<br>libra<ref name=libby/>
|align="right" |
|align="right" | 328.9&nbsp;g&nbsp;
|align="right" | 11.60&nbsp;oz&nbsp;<br>0.725&nbsp;lb&nbsp;
| <small>{{abbr|lit.|literally}}</small>&nbsp;"balance"<ref name=libby>{{Citation |title=Oxford English Dictionary, ''1st ed''. |contribution=libra, ''n.'' |date=1902 |publisher=Oxford University Press |location=Oxford}}.</ref>
|-
| colspan=6 style= "font-size:smaller" | Except where noted, based on Smith (1851).<ref name=smith/> Metric equivalents are approximate, converted at 1 libra = 328.9&nbsp;g&nbsp;.
|-
|}

The subdivisions of the uncia were:

{| class="wikitable" style="margin: 1em auto 1em auto"
|+Subdivisions of the uncia
|-
! Roman unit
! English<br>name
! Equal<br>to
! Metric<br>equivalent
! Imperial<br>equivalent
! Description
|-
| [[siliqua]]
| [[carat (unit)|carat]]
|align="right" | {{frac|1|144}} uncia
|align="right" | 0.19&nbsp;g&nbsp;
|align="right" | 2.9&nbsp;[[Grain (unit)|gr]]&nbsp;<br>0.0067&nbsp;oz&nbsp;
| <small>{{abbr|lit.|literally}}</small>&nbsp;"[[Ceratonia siliqua|carob]] seed"<br>The Greek {{lang|grc|κεράτιον}} (''kerátion'')
|-
| [[obol (coin)#Weight|obolus]]
| obolus<ref name=obladi>{{Citation |title=Oxford English Dictionary, ''3rd ed''. |contribution=obelus, ''n.'' |date=2004 |publisher=Oxford University Press |location=Oxford}}.</ref>
|align="right" | {{frac|1|48}} uncia
|align="right" | 0.57&nbsp;g&nbsp;
|align="right" | 8.8&nbsp;gr&nbsp;<br>0.020&nbsp;oz&nbsp;
| <small>{{abbr|lit.|literally}}</small>&nbsp;"[[obol (coin)|obol]]", from the Greek word for "metal spit"<ref name=obladi/>
|-
| scrupulum
| [[scruple (unit)|scruple]]<ref name=scrup/>
|align="right" | {{frac|1|24}} uncia
|align="right" | 1.14&nbsp;g&nbsp;
|align="right" | 17.6&nbsp;gr&nbsp;<br>0.040&nbsp;oz&nbsp;
| <small>{{abbr|lit.|literally}}</small>&nbsp;"small pebble"<ref name=scrup>{{Citation |title=Oxford English Dictionary, ''1st ed.'' |contribution=scruple, ''n.<sup>1</sup>'' |date=1911 |publisher=Oxford University Press |location=Oxford}}.</ref>
|-
| semisextula or dimidia sextula
|
|align="right" | {{frac|1|12}} uncia
|align="right" | 2.28&nbsp;g&nbsp;
|align="right" | 35.2&nbsp;gr&nbsp;<br>0.080&nbsp;oz&nbsp;
| <small>{{abbr|lit.|literally}}</small>&nbsp;"half-sixth", "little sixth"
|-
| sextula
| sextula<ref name=sexu/>
|align="right" | {{frac|1|6}} uncia
|align="right" | 4.57&nbsp;g&nbsp;
|align="right" | 70.5&nbsp;gr&nbsp;<br>0.161&nbsp;oz&nbsp;
| <small>{{abbr|lit.|literally}}</small>&nbsp;"little sixth"<ref name=sexu>{{Citation |title=Oxford English Dictionary, ''3rd ed''. |contribution=sextula, ''n.'' |date=2008 |publisher=Oxford University Press |location=Oxford}}.</ref>
|-
| sicilicus or siciliquus
|
|align="right" | {{frac|1|4}} uncia
|align="right" | 6.85&nbsp;g&nbsp;
|align="right" | 106&nbsp;gr&nbsp;<br>0.242&nbsp;oz&nbsp;
|<small>{{abbr|lit.|literally}}</small>&nbsp;"little [[sickle]]"
|-
| duella
|
|align="right" | {{frac|1|3}} uncia
|align="right" | 9.14&nbsp;g&nbsp;
|align="right" | 141&nbsp;gr&nbsp;<br>0.322&nbsp;oz&nbsp;
| <small>{{abbr|lit.|literally}}</small>&nbsp;"little double [sixths]"
|-
| semuncia
| half-ounce<br>semuncia<ref name=semunc/>
|align="right" | {{frac|1|2}} uncia
|align="right" | 13.7&nbsp;g&nbsp;
|align="right" | 211&nbsp;gr&nbsp;<br>0.483&nbsp;oz&nbsp;
| <small>{{abbr|lit.|literally}}</small>&nbsp;"half-twelfth"<ref name=semunc>{{Citation |title=Oxford English Dictionary, ''1st ed''. |contribution=semuncia, ''n.'' |date=1911 |publisher=Oxford University Press |location=Oxford}}.</ref>
|-
| uncia
| Roman ounce
|align="right" |
|align="right" | 27.4&nbsp;g&nbsp;
|align="right" | 423&nbsp;gr&nbsp;<br>0.967&nbsp;oz&nbsp;
|style="max-width:0" | "a twelfth"<ref name=uncia/>
|-
| colspan=6 style= "font-size:smaller" | Except where noted, based on Smith (1851).<ref name=smith/> Metric equivalents are approximate, converted at 1 libra = 328.9&nbsp;g&nbsp;.
|-
|}

==Time==
{{unreferenced section|date=November 2011}}

===Years===
The complicated [[Roman calendar]] was replaced by the [[Julian calendar]] in 45&nbsp;BC.<ref>{{cite web|url=https://www.timeanddate.com/calendar/julian-calendar.html|title=The Julian Calendar|website=timeanddate.com|access-date=2019-05-25}}</ref> In the Julian calendar, an ordinary year is 365 days long, and a [[leap year]] is 366 days long. Between 45&nbsp;BC and AD&nbsp;1, leap years occurred at irregular intervals. Starting in AD&nbsp;4, leap years occurred regularly every four years. Year numbers were rarely used; rather, the year was specified by naming the [[Roman consul]]s for that year. (As consuls' terms latterly ran from January to December, this eventually caused January, rather than March, to be considered the start of the year.) When a year number was required, the Greek [[Olympiads]] were used, or the count of years since the founding of Rome, "[[ab urbe condita]]" in 753&nbsp;BC. In the [[Middle Ages]], the year numbering was changed to the [[Anno Domini]] count, based on the supposed birth year of [[Jesus]].

The calendar used in most of the modern world, the [[Gregorian calendar]], differs from the Julian calendar in that it skips three leap years every four centuries (i.e. 97 leap years in every 400) to more closely approximate the length of the [[tropical year]].

===Weeks===
The Romans grouped days into an eight-day cycle called the {{lang|la|[[nundinae]]}}, with every eighth day being a market day.

Independent of the {{lang|la|nundinae}}, [[astrologer]]s kept a seven-day cycle called a ''[[wikt:hebdomas|hebdomas]]'' where each day corresponded to one of the seven [[classical planets]], with the first day of the week being [[Saturday|Saturn-day]], followed by [[Sunday|Sun-day]], [[Monday|Moon-day]], [[Tuesday|Mars-day]], [[Wednesday|Mercury-day]], [[Thursday|Jupiter-day]], and lastly [[Friday|Venus-day]]. Each astrological day was reckoned to begin at sunrise. The [[History of the Jews in the Roman Empire|Jew]]s also used a seven-day week, which began Saturday evening. The seventh day of the week they called [[Shabbat|Sabbath]]; the other days they numbered rather than named, except for Friday, which could be called either the Parasceve or the sixth day. Each Jewish day begins at sunset. [[Christians]] followed the Jewish seven-day week, except that they commonly called the first day of the week the {{lang|la|Dominica}}, or the [[Lord's day]]. In 321, [[Constantine the Great]] gave his subjects every Sunday off, thus cementing the seven-day week into Roman civil society.<ref>{{Cite web |title=Sunday {{!}} Rest, Worship, Reflection {{!}} Britannica |url=https://www.britannica.com/topic/Sunday-day-of-week |access-date=2025-05-21 |website=www.britannica.com |language=en}}</ref>

===Hours===
{{main article|Roman timekeeping}}
The Romans divided the daytime into twelve ''horae'' or [[hour]]s starting at sunrise and ending at sunset. The night was divided into four watches. The duration of these hours varied with seasons; in the winter, when the daylight period was shorter, its 12 hours were correspondingly shorter and its four watches were correspondingly longer.

Astrologers divided the [[solar day]] into 24 equal hours, and these astrological hours became the basis for medieval [[clock]]s and our modern 24-hour [[mean solar day]].

Although the division of hours into [[minute]]s and [[second]]s did not occur until the Middle Ages, [[Classical antiquity|Classical]] astrologers had a ''minuta'' equal to {{frac|60}} of a day (24 modern minutes), a ''secunda'' equal to {{frac|3600}} of a day (24 modern seconds), and a ''tertia'' equal to {{frac|216,000}} of a day (0.4 modern seconds).

==Unicode==
{{special characters|unicode}}
{{Main article|Ancient Symbols (Unicode block)}}
{{see also|Unicode input}}
A number of special symbols for Roman currency were added to the [[Unicode]] Standard version 5.1 (April 2008) as the Ancient Symbols block (U+10190–U+101CF, in the Supplementary Multilingual Plane ).

{{Unicode chart Ancient Symbols}}

As mentioned above, the names for divisions of an {{lang|la|as}} coin (originally one libra of bronze) were also used for divisions of a libra, and the symbols U+10190–U+10195 are likewise also symbols for weights:
* '''U+10190 (𐆐):''' Sextans
* '''U+10191 (𐆑):''' Uncia
* '''U+10192 (𐆒):''' Semuncia
* '''U+10193 (𐆓):''' Sextula
* '''U+10194 (𐆔):''' Semisextula
* '''U+10195 (𐆕):''' Siliqua


==See also==
* [[Ancient Egyptian units of measurement|Ancient Egyptian units]]
* [[Ancient Greek units of measurement|Ancient Greek units]]
* [[Biblical and Talmudic units of measurement]]
* [[Byzantine units]]
* [[History of measurement]]

==Notes==
{{notelist}}
==References==
{{reflist|refs=

<ref name=brit>Hosch, William L. (ed.) (2010) [https://books.google.com/books?id=cuN7rH6RzikC ''The Britannica Guide to Numbers and Measurement''] New York: Britannica Educational Publications, 1st edition. {{ISBN|978-1-61530-108-9}}, p. 206</ref>

<!--unused<ref name=brit2>{{cite book |title=Encyclopædia Britannica almanac 2008|url=https://books.google.com/books?id=0EniB-D24w4C&pg=PA162|year=2009|publisher=Encyclopædia Britannica|isbn=978-1-59339-475-2|page=162}}</ref>-->

<!--unused<ref name="card">{{cite book | url=https://archive.org/details/encyclopaediaofs0000card | url-access=registration | title=''Encyclopaedia of Scientific Units, Weights and Measures: Their SI Equivalences and Origins'' | publisher=Springer | authors=Cardarelli, François; M.J. Shields (tr.) | year=2003 | pages=[https://archive.org/details/encyclopaediaofs0000card/page/74 74]–5 | isbn=9781852336820}}</ref>-->

<ref name=front>Sextus Julius Frontinus (c. 100 AD) [https://penelope.uchicago.edu/Thayer/L/Roman/Texts/Frontinus/De_Aquis/text*.html#1.24 ''De aquis'' '''1''':24] (Latin). [https://penelope.uchicago.edu/Thayer/E/Roman/Texts/Frontinus/De_Aquis/Rodgers/1**.html#1.24 ''De aquis'' '''1''':24] (English translation).</ref>

<ref name=greaves>[[John Greaves|Greaves, John]] (1647) [https://archive.org/details/bub_gb_LW86AAAAcAAJ ''A discourse of the Romane foot and denarius; from whence, as from two principles, the measures and weights used by the ancients may be deduced''] London: William Lee</ref>

<ref name=Millar>Lucius Junius Moderatus Columella, Anon. (trans.) (1745) [https://books.google.com/books?id=qcNbAAAAMAAJ ''L. Junius Moderatus Columella of Husbandry, in Twelve Books: and his book, concerning Trees. Translated into English, with illustrations from Pliny, Cato, Varro, Palladius and other ancient and modern authors''] London: A. Millar. pp xiv, 600 [208–216].</ref>

<ref name=skinner>{{cite book|last=Skinner|first=Frederick George|title=Weights and measures: their ancient origins and their development in Great Britain up to A.D. 1855|url=https://books.google.com/books?id=bDcLAQAAIAAJ&q=roman+pound+5076+grains|access-date=9 December 2011|year=1967|publisher=H.M.S.O.|page=65|isbn=9789140059550}}</ref>

<ref name=smith>Smith, Sir William; Charles Anthon (1851) [https://books.google.com/books?id=uUPhhcdSACQC ''A new classical dictionary of Greek and Roman biography, mythology, and geography partly based upon the Dictionary of Greek and Roman biography and mythology''] New York: Harper & Bros. Tables, pp. 1024–1030</ref>

<ref name=zupko>{{cite book|last=Zupko|first=Ronald Edward|author-link=Ronald Edward Zupko|title=British weights & measures: a history from antiquity to the seventeenth century|url=https://books.google.com/books?id=pWUgAQAAIAAJ&q=5076|access-date=9 December 2011|year=1977|publisher=University of Wisconsin Press|page=7|isbn=9780299073404}}</ref>

}}

==External links==
* [http://std.dkuug.dk/JTC1/SC2/WG2/docs/n3138.pdf Proposal to Add Ancient Roman Weights and Monetary Signs to UCS (Universal Character Set)]

{{Systems of measurement}}

[[Category:Ancient Roman units of measurement| ]]