This resource is an archived version of the Readability Guidelines.

New wiki is at:
Go to the Numbers page.



Use ‘one’ unless you’re talking about a step, a point in a list or another situation where using the numeral makes more sense: ‘in point 1 of the design instructions’, for example. Or this:

You’ll be shown 14 clips that feature everyday road scenes.

There will be:

1 developing hazard in 13 clips
2 developing hazards in the other clip

Write all other numbers in numerals (including 2 to 9) except where it’s part of a common expression like ‘one or two of them’ where numerals would look strange.

If a number starts a sentence, write it out in full (Thirty-four, for example) except where it starts a title or subheading.

For numerals over 999, insert a comma for clarity: 9,000

Use a 0 where there’s no digit before the decimal point.

Avoid using or write out 0 (zero) and 1 (one) where they could cause confusion with the letters "O" and "I" or "l".

Fractions and percentages

Spell out common fractions like one-half.

Use a % sign for percentages: 50%

Use MB preceded by a space for anything over 1 MB: 4 MB not 4096 KB.

Use KB preceded by a space for anything under 1 MB: 569 KB not 0.55 MB.

Keep it as accurate as possible and up to 2 decimal places: 4.03 MB.


Use ‘500 to 900’ and not ‘500-900’.

Addresses: use ‘to’ in address ranges: 49 to 53 Cherry Street.


For most audiences, writing the year followed by the month is most comprehensible. For example: '1 year 6 months' rather than '18 months', 'a year and a half' or '1.5 years'.

Below 1 year, use months e.g. 6 months old.


Use a clear and familiar typography. 1 and I can look the same depending on the typeface.


Be specific and again, consider the context.
20% of 10 people is very different to 20% of 100.

Usability evidence

'The innate mind: Structure and Contents Part III > Number and natural language', 2005

'Formatting the value of a quantity', 2006

'Show numbers as numerals when writing for online readers', 2007

'Knowledge of number and knowledge of language: Number as a test case for the role of language in cognition', 2008

GOV.UK Style guide A to Z, UK Government, 2016

GOV.UK Content principles, UK Government, 2016

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