Numbers

Numerals or letters

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.

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.

Ranges

Use ‘500 to 900’ and not ‘500-900’ (except in tables).

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

Ages

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.

0O and 1I

Avoid using or write out 0, O, 1 and I where they could cause confusion.

Typography

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

Data

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

References

GOV.UK style guide: https://www.gov.uk/guidance/style-guide/a-to-z-of-gov-uk-style
Formatting the value of a quantity (Bureau International des Poids et Mesures): https://www.bipm.org/en/publications/si-brochure/section5-3-3.html
Evidence: https://www.gov.uk/government/publications/govuk-content-principles-conventions-and-research-background/govuk-content-principles-conventions-and-research-background
Show numbers as numerals when writing for online readers: https://www.nngroup.com/articles/web-writing-show-numbers-as-numerals/

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