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)