kilogram, kg, kilo

SI (International System of Units) usage, followed in scientific and technical writing, requires that both the number and unit name be written in full (e.g. twelve kilograms) or that the numeral be followed by the symbol (e.g. 12 kg).

• This lighter dumbbell weighs two kilograms.
• A male Great Dane may weigh up to 90 kg.

However, general usage accepts numerals with spelled-out unit names (e.g. 12 kilograms) to improve comprehension. When no specific figure is stated, write kilogram in full. Kilo is an informal term for kilogram.

• How many kilograms does your St. Bernard weigh? He weighs 60 kilos (or 60 kilograms).

Symbol kg

Because the metric (SI) system uses symbols, not abbreviations, the symbol kg is not followed by a period and does not take an s in the plural.

• Each sack of cement weighs 25 kg (not 25 kgs).

The unit symbol kg and the prefix kilo are in lower case, even when the rest of the text is in upper case, as in a newspaper headline.

• The tabloid article was entitled “HEAVIEST CAT ON RECORD WEIGHS 25 kg.”

Modifier

For the sake of clarity, when kilogram is used as a modifier, a hyphen is inserted between the number and the unit name:

• Gertrude bought Conrad a two-kilogram (or 2-kilogram) box of chocolates as a get-well gift.

However, do not insert a hyphen if the unit symbol is used in place of the unit name:

• Henry picked up the 12 kg bag of potatoes with ease.