The names of metric units are usually spelled out.
- A 20-kilogram sack, not a 20-kg sack
- He ran 10 kilometres, not he ran 10 km
There are no abbreviations in metric, only symbols. These symbols take periods only at the end of a sentence, never take an s in the plural and are separated from a number by a space. Metre is m, kilometre is km, kilogram is kg, Celsius is C, metric tonne is t, hour is h. Only Celsius is capitalized as C.
- He drove 10 km to the store.
- The weather was a sunny 23 C on Wednesday.
Use a hyphen when indicating a metric quantity as an adjective.
- a 10-kilogram sack
C (for Celsius) can be used on first reference. Other common symbols such as km/h, mm and KB should be written out on first reference but may be used on second reference when preceded by a number at 70 km/h, a 105-mm cannon, a 112-KB file.
A number less than one has a zero before the decimal.
Symbols may be used in charts, graphics, tables and the like, as well as in coverage of certain sports.
Write the numbers one to nine as words. The same goes for first to ninth.
Write the numbers 10 and up as numerical figures.
- 3,500 26 99th 10th
When the number is four digits or longer, separate with commas rather than spaces or periods.
- 100,000 not 100 000 or 100.000
- There are 1,200 students.
- A $430,000 grant
For large numbers, it is better to use words or a combination of words and numbers. Write 1.4 million rather than 1,400,000. Write one million rather than 1,000,000.
For the plural of numbers, including decades, do not use an apostrophe before the “s.”
- The 1960s were exciting.
- Give me all the 10s and 20s.
For numbers in official names, follow the organization’s spelling style:
- 7Up
Do not use commas with dimensions, measurements and weights consisting of two or more elements.
- A woman is five feet 11 inches tall; a trip of six months three weeks two days; in two hours 21 minutes 45 seconds
When to use figures:
- In addresses, in ages standing alone after a name, in dates and years, in decisions, rulings, scores, votes and odds, in monetary units preceded by a symbol, in temperatures, in times, for latitude and longitude.
When to spell out:
- At the start of a sentence, if you must start with a number.
In headlines:
- Use numerals for numbers under 10.
- Use numerals – 8 instead of eight, 1st instead of first, etc. – for numbers under 10.
- Use M, capped, for million after numeral.
- $2M in funding.
(For percentages, see the Spelling section. For more on headlines, see Headlines section.)
Don’t use ordinal indicators (the suffixes "st," "nd," "rd," "th") when writing dates.
- Oct. 12 not Oct. 12th or Oct. 12th
Spell out if below 10.
- She placed eighth in the spelling bee
- He finished 15th in the race
Don’t use superscript unless as a design element.
- 24th not 24th