C18

C18 may refer to:

Science and technology

• Caldwell 18 (NGC 185), a dwarf spheroidal galaxy of the Local Group in the constellation Cassiopeia
• Carbon-18 (C-18 or ¹⁸C), an isotope of carbon
• Template:Chem/link, the molecular formula of cyclo(18)carbon
• C18, an octadecyl-type hydrocarbon with 18 carbon atoms, such as
  • Fatty acids such as
    • Stearic acid, C₁₈H₃₆O₂
    • Oleic acid C₁₈H₃₄O₂
  • C18 bonded silica stationary phase column, a type of reversed-phase chromatography column
• IEC 60320 C18, a power connector
• Colorectal cancer (ICD-10 code)
• ISO/IEC 9899:2018 standard for the programming language C, informally named C18

Transportation and military

• HMS C18, a submarine
• Sauber C18, a Formula One racing car
• Chrysler Royal C18, a 1938 car
• The C-18, a military cargo version of the Boeing C-137 Stratoliner

Other uses

• French Defence (Encyclopaedia of Chess Openings code)
• Combat 18, a British neo-Nazi organization
• 18th century (1701–1800 AD)
• Android 18, character from Dragon Ball Franchise
• Bill C-18, Canada's Online News Act