Rates
A simple rate involving 2 units can be expressed in 1 of 2 ways: with unit symbols, using / (see also Dashes, slashes and ellipses), or in words, using per:
3 t/ha 3 tonnes per hectare
Do not use any of the following expressions:
3 t per ha [do not use per with symbols]
3 t per hectare 3 t/hectare [do not mix symbols and words in units]
Ensure that it is clear what the unit applies to:
nitrogen was applied at 3 t/ha
not
3 t/ha of nitrogen was applied [could imply hectares of nitrogen]
sodium at a concentration of 25 mg/mL
not
25 mg/mL of sodium [could imply mL of sodium]
Dimensions
For dimensions, use a multiplication symbol with nonbreaking spaces on either side; include the unit after each number:
3 m × 3 m
Caution! The multiplication symbol (×) is a specific symbol, not a lower-case x.