Should There Be a Space Before Units?

The numerical value always precedes the unit, and a space is always used to separate the unit from the number.

Do you put a space before a unit?

There is a space between the numerical value and unit symbol, even when the value is used in an adjectival sense, except in the case of superscript units for plane angle. If the spelled-out name of a unit is used, the normal rules of English apply: "a roll of 35-millimeter film."

Should there be a gap between number and unit?

There is a space between a number and a unit of measurement e.g. 20 mg – except for temperatures e.g. 20°C and percentages e.g. 20% (or in text use 20 per cent). When giving a range do not repeat the unit, e.g. 5 to 8 mg and not 5 mg to 8 mg. Use the word 'to' in text, not a dash.