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%

Phases of clinical trials

When referring to clinical trials, please use roman numerals (e.g. I, II, III) rather than numbers or words.

For example:

  • We will seek to start Phase III of this trial in January 2020, but only if the results from Phase II are promising.

Telephone numbers

In print

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, brackets should be placed around the international code. Do not include brackets around the first number.

For example:

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

Find out more

Learn more about using dashes and hyphens.