Rules for writing numbers

While writing numbers, sometimes we use figures or digits and sometimes we write out the number in words. Here is a quick overview of the rules for writing numbers.

Small numbers

Numbers smaller than ten should be spelled out.

Two birds were sitting on a branch. (NOT ‘2 birds were sitting on a branch.’)

Two-word numbers should be expressed in figures. Examples are: 24, 32, 56 etc.

I got only 35 marks in English. (More natural than I got only thirty-five marks in English.)

One-word numbers can be spelled out. Examples are: eleven, thirteen, twenty, thirty etc.

When writing large number we often use commas.

There are 746,372 voters in this constituency.

The period is used as a decimal separator. Example: 10.5

The International Systems of Units (SI) does not recommend the use of commas or periods.

SI recommends that a space should be used to separate groups of three digits.

He earns $1 500 000 a year.

You cannot begin a sentence with a numeral.

Write ‘Twenty years ago…’ (NOT 20 years ago…)

Sometimes you will have to change the structure of the sentence to remove the numeral from the beginning.

Write ‘They sold 400,000 copies on the first day’ instead of ‘400,000 copies were sold on the first day.’

Centuries should be spelled out.

In the nineteenth century

But some writers also use a combination of numbers and letters. Example: 19th century

Percentages

In a less formal style, you can use the symbol %. In formal writing, you should spell the percentage out.

She got 96% marks. (Informal)

She got 96 percent marks. (Formal)