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
 * , 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