Numbers up to and including ten should be spelled out in full. Numbers after and including 11 should be written using numerals.

Very large numbers should be written by combining a figure and a word such as million or billion.

Fractions should generally be written in full and hyphenated in prose. In a table or list, numerals should be used.

If a sentence begins with a number, it is preferable to spell that number out, even if it is a number above 11.

Within a single sentence, when talking about the same unit, consistency in use of written vs. numerals is preferred, even if this means disregarding the house style.

For example:

  • Imperial awarded honorary degrees to two individuals in May 2015; Professor Frank Kelly and Professor Elizabeth Simpson.
  • Schistosomiasis affects 240 million people, and each year an estimated 280,000 people die from the disease.
  • In 2014, approximately 12,000 people visited the Imperial Festival.
  • Of 50 students surveyed, just 4 reported dissatisfaction with the service provided.
  • Fifteen Imperial students participated in the competition.
  • Two-thirds of participants in the study reported reduced side effects.

More numbers


Both ‘per cent’ and ‘%’ are acceptable, providing use is consistent throughout a piece of writing. In general, ‘per cent’ is preferable in prose, and ‘%’ is preferable in tables or lists.

For example:

  • In total, 60 per cent of Imperial responded to the 2014 staff survey.
  • The survey asked staff whether they had experienced an unreasonable level of pressure at work. Results were as follows:
  1. Never: 24%
  2. Infrequently: 30%
  3. Some of the time: 34%
  4. A lot of the time: 12%

Telephone numbers

In printed material, telephone numbers should generally include the international code. For UK numbers, the first number should appear in brackets (as it is only used when a number is dialled within the UK), and spaces should be included after the area code and after the fourth number.

For example:

  • To find out more, please call +44 (0)20 7589 5111

 In online material, do not use brackets around the first number, use brackets around the international code.

For example,

  • To find out more, please call (+44) 020 7589 5111

For more information: