Guide for the Use of the International System of Units (SI)

Guide for the Use of the International System of Units (SI) 
 
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Example:
pascal second or pascal-second 
9.5 Spelling unit names obtained by division 
 
When the name of a derived unit formed from other units by division is spelled out, the word “per” is used 
and not a solidus. (See also Secs. 6.1.7 and 9.8.) 
Example:
ampere per meter (A/m)
but not:
ampere/meter 
 
9.6 Spelling unit names raised to powers 
 
When the names of units raised to powers are spelled out, modifiers such as “squared” or “cubed” are used 
and are placed after the unit name.
Example:
meter per second squared (m/s
2
) 
The modifiers “square” or “cubic” may, however, be placed before the unit name in the case of area or 
volume. 
Examples: square centimeter (cm
2
)
cubic millimeter (mm
3
) 
ampere 
per 
square 
meter 
(A/m
2
)
kilogram per cubic meter (kg/m
3
) 
9.7 Other spelling conventions 
 
A derived unit is usually singular in English, for example, the value 3 m
2
·K/W is usually spelled out 
as “three square meter kelvin per watt,” and the value 3 C·m
2
/V is usually spelled out as “three coulomb 
meter squared per volt.” However, a “single” unit may be plural; for example, the value 5 kPa is spelled out 
as “five kilopascals,” although “five kilopascal” is acceptable. If in such a single-unit case the number is 
less than one, the unit is always singular when spelled out; for example, 0.5 kPa is spelled out as “five-
tenths kilopascal.”
Note: These other spelling conventions are given for completeness; as indicated in Sec. 7.6, it is the 
position of this Guide that symbols for numbers and units should be used to express the values of 
quantities, not the spelled-out names of numbers and units. Reference [3] also requires that a 
symbol for a number be used whenever the value of a quantity is expressed in terms of a unit of 
measurement.