Units of measurement Wikipedia:Manual of Style

the main unit in quantity expressed should si unit or non-si unit officially accepted use si. however,

scientific articles may use specialist units appropriate branch of science in question.
in non-scientific articles relating united states, main unit u.s. customary unit (22 pounds (10 kg)).
in non-scientific articles relating united kingdom, although main unit metric unit (10 kilograms (22 lb)), imperial units still used main units in contexts (7 miles (11 km) road).


where english-speaking countries use different units same measurement, provide conversion in parentheses. examples: mississippi river 2,320 miles (3,734 km) long; murray river 2,375 kilometres (1,476 mi) long. {{convert}} template useful producing such expressions.
in direct quotation, retain source s units. conversion should follow in square brackets (or, obscure use of units can explained in footnote).
where space limited (such tables, infoboxes, parenthetical notes, , mathematical formulas) unit symbols preferred. in prose, unit names should given in full if used few times symbols may used when unit (especially 1 long name) used repeatedly after spelling out first use (e.g. 15 kilograms of filler used batch of 250 kg), except unit names hardly ever spelled out (°c rather degrees celsius).
most unit names not capitalized. (for spelling differences, follow § national varieties of english, above.)
use per when writing out unit, rather slash: metre per second, not metre/second.
units unfamiliar general readers should presented name–symbol pair on first use, linking unit name (energies 2.3 megaelectronvolts (mev), 6 mev).
for ranges, see § en dashes: other uses, above, , mos:num, @ §§ date ranges, percentages, unit names , symbols, , formatting of monetary values.
unit symbols preceded figures, not spelled-out numbers. values , unit symbols separated non-breaking space. example, 5 min. percent sign , units of degrees, minutes, , seconds angles , coordinates unspaced.