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Part of: Grammar points


Last updated: 20 December, 2019

Following this helps people with:

  • time pressures: numerals and specific data are quicker to scan read

  • stress: not having to decipher fractions is easier and less stressful

  • multi-tasking: clear, specific data is easier to absorb

  • cognitive impairments: numerals carry less cognitive load

  • visual impairments: with a limited field of visual focus, numerals may stand out more


Number presentation style affects readability and usability. These recommendations help make facts you’re conveying through data clear to your users. 

1. Use numerals instead of words for numbers.

2. Choose clear typography.

3. Be specific with data.

4. Use percentages.

5. Use "to" for number ranges, not a hyphen.

6. Use years and months not just months.

7. Use a space before KB and MB.

8. Spell out month in dates, write day as a numeral without "st", "nd" or "th".

Usability evidence

1. Use numerals instead of words for numbers.

They are easier to scan read. It's more consistent to always use numerals rather than have a variety of rules for different sentence structures.


"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"

2. Choose clear typography.

"1" and "I" can look the same depending on the typeface, as can "0 and "O", so choose a typeface where these characters look sufficiently different and unique. Test with users if you're not sure.

Avoid using 0 and 1 if they could cause confusion with letters. Make sure passcodes do not include characters that can cause letter confusion.

3. Be specific with data.

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


"20 people" not "20% of the survey group"

Keep data as accurate as possible, 2 decimal places is recommended.


4.03 MB

4. Use percentages.

Use a % sign for percentages: 50%


Use "500 to 900" and not "500-900".

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

6. Use years and months not just months.

For most audiences, writing the year followed by the month is most comprehensible.


"1 year 6 months" not "18 months", "a year and a half" or "1.5 years".

Below 1 year, use months: 

"6 months old"

7. Use a space before KB and MB

Use KB with a space before for anything under 1 MB. Use MB with a space before for anything over 1 MB.


569 KB not 0.55 MB
4 MB not 4096 KB

8. Write dates without "st", "nd", "th", known as cardinals.

Do not use a comma to separate the year. Write the year in full. Spell out the month.

Example for UK:

18 July 2019

Example for US:

July 18 2019

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', J. Nielson, 2007

'Knowledge of number and knowledge of language: Number as a test case for the role of language in cognition', De Cruz, H. and Pica, P., 2008. Locked

'Low levels of numeracy are a long-term problem for the UK', National Numeracy update, National Numeracy YouGov Survey 2014, data sources: Skills for Life 2011PIAAC 2014,

GOV.UK Content principles, UK Government, 2016

GOV.UK Style guide A to Z, Dates and number ranges, UK Government, 2016

'Numeracy and decision making’, Peters, E., D. Västfjäll, et al., Psychological Science, 17(5), pp. 407 to 413. 2006. Locked. Related free access article 'Affect and decision-making: a "hot" topic', Peters, E., D. Västfjäll, Gärling, T., Slovic, P.

'Less is more in presenting quality information to consumers', Peters, E., N. Dieckmann, et al, Medical Care Research and Review, 64 (2), pp.169 to 190. 2007

'‘‘A 30% chance of rain tomorrow’’: How does the public understand probabilistic weather forecasts?', Gigerenzer, G., Hertwig, R., van den Broek, E., Fasolo, B., & Katsikopoulos, K.V., Risk Analysis, 25, 623 to 629, 2006

'The Effect of Type Size and Case Alternation on Word Identification’, Smith, Lott and Cronnell, 1969. Semi-locked: free to access online with MyJSTOR account.

'Case alternation impairs word identification’ Coltheart, M. and Freeman, R. 2013

'Letter and symbol misrecognition in highly legible typefaces for general, children, dyslexic, visually impaired and ageing readers', Thomas Bohm, 4th edition, 2019. More typography writing and papers from User Design.

'Web style guide' Chapter 9. Typography, Typefaces section, Lynch, P. and S. Horton, 4th edition, 2016

Relevant wiki content

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