Tips on writing whole numbers, decimals, fractions, percentages, dates, and time.
Spell out numbers from one to nine; use digits for numbers 10 and greater. Where numbers in a range span this cut-off, use a consistent form (preferably digits): for example, “from 8 to 12” or “from eight to twelve” (not “from eight to 12”).
To reduce any possibility of confusion, always express the numbers of a range in full: for example, “from $10 thousand to $50 thousand” (not from “$10 to $50 thousand”); “between 6 million and 18 million” (not “between 6 and 18 million”).
Use a comma (not a point or space) to set off thousands/millions in whole numbers: for example, “6,800”, “25,612”, “25,612,800”.
Use “billion” to mean a thousand million (1,000,000,000), and “trillion” to mean a thousand billion (1,000,000,000,000). (In older British usage, “billion” was equivalent to a million million while “trillion” was equivalent to a million million million.)
If a number begins a sentence, spell it out in full.
Use a point (not a comma) to separate whole numbers from decimals: for example, “3.14159”, “6.8”, “25.612”.
When giving a range of (or comparing) decimal statistics, use the same number of decimal places for each to ensure clarity. In particular, don’t drop the final zero(s): for example, “from 3.00 to 6.72” (not “from 3 to 6.72”); “3.14–12.20 (not “3.14–12.2”) .
Use a hyphen when a fraction is used as an adverb or adjective, but not when it is used as a noun: for example, “a one-tenth increase”, but “an increase of one tenths”; “a two-thirds majority voted in favour”, but “two thirds of the members voted in favour”).
Use “per cent” (two words, with a preceding space) for percentages written in word form: for example, “six per cent”, “twenty per cent”. Use the % symbol (without a preceding space) for percentages written as digits: for example, “3.8%”, “25%”. Either style is acceptable, be consistent; do not mix these two forms within a publication.
To avoid potential confusion regarding dates, always use the form “day month year”, with no comma between the month and year: for example, “21 April 2004”, “4 July 1776”, “18 September 2014”.
An all-numerical date may cause confusion. For example, a date written as “1/7/2011” would be read as “January 7, 2011” by American readers but as “1 July 2011” by British readers.
Use cardinal, not ordinal, numbers for dates: for example, “4 July 1776”, “1 July 1867” (not “4th July 1776″, “1st July 1867”).
Write time in the following form: “9:30 a.m.”, “12:01 p.m.”, “5:30 p.m.”, “12 noon” (or 12 m., not “12:00 p.m.”), “12 midnight” (not 12:00 a.m.).