Numbers can be tricky – do you write them as figures (1,2,3, etc.) or do you write them as words (one, two, three, etc.)? How do you hyphenate compound words containing numbers? How do you deal with a mixture of figures and words? Dealing with numbers is important for clarity and readability in all forms of writing. We can’t set out every single rule here but the following basic rules should help:
- In formal writing, a general rule of thumb is to write out the numerals one to ten/twelve/twenty then to use numbers thereafter. These thresholds can change according to the nature of the text.
- With a mixture of words and numerals, use words for one quantity and figures for the other (planning permission was granted for five 4-bedroom houses).
- Compound numbers and nouns take a hyphen: twenty-six, thirty-seven, a two-pound coin, a five-litre bottle.
- A comma is used in numerals of more than four digits: 1,000 (in the US the comma is omitted). Large round numbers can be expressed in figures or words (20 million or twenty million).
- Always spell out ordinal numbers (first, second, third, etc.).
- Always use figures for house/building numbers (15 Acacia Drive), scores (they won 4–2), race distances (the 800 metres) and page/chapter numbers (p. 19, Chapter 4).
- Don’t start a sentence with a numeral. Instead of 250 people were killed in the explosion, write Two hundred and fifty people were killed in the explosion.
- If numbers are pluralized, don’t use an apostrophe (the 1980s).
- If it’s a cardinal number (one, two, three, etc.), use a figure (a three-year-old boy). In a compound which is already hyphenated, use figures (a 33-year-old man, not a thirty-three-year-old man). If it’s an ordinal number or a decade (first, second, third, teens, forties, etc.) use words (in her twenty-first year, in his teens).
- In all-figure form, dates are expressed as 16/05/1972 or 16/05/72 (but be careful with US English where this date would be 05/16/72). Cardinal numbers (16 May 1972) are used rather than ordinal numbers (16th May 1972). Again, be careful in US English where the day and month are inverted and have a comma (May 16, 1972). But a comma is used in UK English with a named day (Friday, 16 May 1972).
- Centuries can be in figures, words or abbreviations (tenth century, 10th century, 10th cent., 10th c.). If used adjectivally before a noun, it will need to be hyphenated (tenth-century armour).
- There are numerous eras, the most common of which are AD and BC. They are both written in small caps. BC comes after the figures, AD comes before the figures except where they are written in words (AD 100, 100 BC, the first century AD).
- Use figures (followed by a space) with a.m. and p.m. (4 p.m., 8 a.m.). Only use o’clock with the exact hour (six o’clock). Use full words and hyphens with exact hours or fractions of an hour (a quarter to ten, half past two).
- Fractions used to be written with hyphens but you will see them with and without nowadays i.e. three-quarters or three quarters. Always write out fractions in formal writing.
- Don’t use a hyphen between a whole number and a fraction (two and three-quarters). While a half-mile is hyphenated, half a mile or one and a half miles are not hyphenated.
- They are generally written in figures, either with per cent or %(30% or 30 per cent).
- Symbols always precede the figures (£10, $6 m). Do not use £ and p together.
- If you are using units of measurement, proportion and quantity, the general rule is to use figures (we shared the winnings 60–40, 30 per cent of men).
- In abbreviated units figures are used, followed by a space (10 kg, 12 p.m., 25 cm).
If you find that you don’t know how to express a number, you can always try rephrasing the sentence. Or consult us here at Full Proof – we are a proofreading company with over 15 years’ experience dealing with the best ways to express your written work, to ensure that your numbers are expressed clearly and consistently.