Numbers in general text
For general descriptive or narrative text, use words for numbers from zero to one hundred and the numerical form for 101 and above.
Numbers in technical or scientific writing
If the document is for a technical or scientific audience, numbers between one and nine are spelt out and numbers over 10 are written in their numerical form.
An exception to this is when a number starts a sentence. You would not write ‘25 people attended the event’. It makes better sense to write ‘Twenty five people attended the event’.
The numerical form of numbers is also used in tables, in equations and rations and when you need to show decimal fractions.
If a sentence has the numbers one to five and 26 and 36, for consistency, it is better to spell out each number so that it would look like this ‘one to five and twenty six and thirty six’.
To ensure consistency when writing numbers in multiple publishing projects and publications, include the numbers style parameters in an in-house style guide that is accessible to every production team member.