Writing SI quantities and unit symbols
Symbol form, spacing and parentheses preserve the meaning of reported quantities.
Key knowledge
Write SI unit symbols upright and with their prescribed case; symbols have no plural endings or abbreviation periods. Separate the numerical value from its unit with a space, including °C. Plane-angle °, ′ and ″ are exceptions to that space. Attach a prefix directly to its unit symbol. Use a space or centred dot for multiplied units, and parentheses or negative exponents to make divisions unambiguous.
Conditions and scope
- Unit symbols are distinct from quantity symbols, which are conventionally italic.
- A sentence-ending full stop is ordinary punctuation; it is not an abbreviation mark within a unit symbol.
Sources · 2
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
SI symbols, prefixes, unit products and quotients, and numerical-value spacing follow distinct writing conventions.
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Foundational review
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Sources from other places
Agreement within this scope
SI uses case-sensitive upright unit symbols, unambiguous products/quotients and prescribed number–unit spacing.
Plane-angle degree/minute/second symbols are the spacing exception; Celsius values still need a space.
Inmetro and Instituto Português da Qualidade
- O Sistema Internacional de Unidades (SI) · 2ª edição luso-brasileira Brazil and PortugalPortugueseShared standard
5.2; 5.4.1–5.4.3, pp23–26
- O Sistema Internacional de Unidades (SI) · 2ª edição luso-brasileira
Entry details
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