Rules for Writing Numbers | When to Write Numbers in Words? - UK Rules (2024)

When Should You Write Numbers as Words?

In this section, we list the key guidelines for writing numbers and the general rules for numerals (e.g. spelling numbers as words).

It will help you learn how and when to express whole numbers and when to spell them in your business writing.

Few writers understand when you should use figures (aka digits) and when it is proper to write out the number in words – using letters.

So for example, should you write the positive integer ‘5’ as a figure? Or, do formal writing ethics dictate that it is better to write the number ‘five’ spelled out as a word?

Writing Rules for Numbers

There are a few basic guidelines to follow when expressing arithmetical values in business letters, essays, and in reports. These rules on writing numbers will ensure you use numbers and numerals in the correct way.

The key importance for writers is deciding whether to insert a full phrase or not. Thus, you could write it as one hundred thousand three hundred and nine (for example). Or, should you use numerals and write it using digits – as in 100,309?

Here’s how it works:

The guiding rules for general writing suggest you should almost always use full words for small numbers, from one to nine (i.e. not 1, 2, 3, to 9), and numerals for those over nine.

As a rule of thumb, use written words if it can be expressed in two words or less. But, remember that many will require a hyphen, such as ‘thirty-nine’.

The regulations vary, and get a little confusing, for the large symbols. Even so, one rule for writing numbers that seems to be universally agreed upon, is that you should never start a sentence with a number.

Note: You must try to avoid torturing your readers. We recommend rewriting a sentence instead of working with long digitized integers or a combination of complex numerals.

Number versus Numeral

So, what is the key difference between a number and a numeral? A number is an abstract concept. Whereas, a numeral is a symbol used to express it.

For example the word ‘three’, the positive integer ‘3’, and the numeral ‘III’ are all symbols used to express the concept of ‘three-ness’.

Writing Numbers Rules

Always use numerals:

• In dates (e.g. Wednesday 27 January, 2016).
• For decimals and fractions (3.425, 1/4 inch, 1/2 a pint, 0.75).
• Except when the figures are vague (…almost half the voters in the country).
• Before anything that can be measured (4 decades, 2 years).
• When using a single digit number and another composed of two or more digits in the same sentence.
• If it modifies a unit of measurement, time or proportion (8 minutes, 5 kilograms, 49 mph).

Note: Another article highlights the key benefits of National Numeracy Day events in the United Kingdom. Learn how to be more number confident and where to find some helpful resources.

When to Use a Comma

In written English, we use a comma to separate thousands and as the period separator in decimals. The primary purpose of commas is to make large numbers easier to read.

For example:

Instead of writing the size of the United Kingdom as 243610 square kilometers, it would be better to express it as 243,610 square kilometers (or even km²).

The International Systems of Units (SI) recommends a space to separate groups of three digits. The comma and the period should be used only to denote decimals, such as $14 300,75.

Spell Out Centuries and Decades

When you are writing about periods of time, such as centuries or decades, you should spell them out. Hence, it should be… during the ‘seventies’ or in the ‘twentieth century’ – for example.

Percentages and Food Recipes

You can use some digits with informal everyday writing. Thus, jotting a recipe as ‘mix 3 cups of jasmine rice’ is absolutely fine.

But, you should be spelling out the percentage, such as in ‘eight percent of the population’ when using formal communication.

Expressing a percentage such as ‘8% of the population’ should only be written for visual presentation – such as in business use.

Rounding Numbers and Estimations

Numbers rounded higher than one million should be written as a numeral plus a word. Hence, write ‘around 300 million people’ instead of ‘around 300,000,000 people’. Simply put, exact numbers should always be written.

Repeating Numbers

Two consecutive numbers placed next to each other is very confusing. Instead of scribbling something like, ‘9 15-year-olds’, write one as a numeral. So, it would become ‘nine 15-year-olds’.

Thus, it is easier to understand (and makes more sense) if you choose to script the number which has the fewest letters.

Cardinals and Ordinals

As a rule, it would be inconsistent to state something like ‘She was my 1st true love’. Writing ‘She was my first true love’ is using extra consistency in the sentence.

This works best when the cardinal numbers relate to each other. So, spell it out when used in a quote, such as ‘…four score..’ and not ‘…4 score..’

Related English Writing Help Guides

• Acronym rules (includes examples of acronyms).
• Do bullet points need periods?
• Email etiquette UK (writing for business communication).

Note: The short video explains how to express numbers in your writing with ten simple rules for writing numbers and numerals.

Footnote: Expert authors and formal writers do not always agree on the rules of writing numbers and numerals. In fact, there does not seem to be one single standard that all literary professionals follow. Even so, we hope this section helped your understanding of the basic principles of spelling out numbers.

When Should You Be Writing Numbers as Words in Written English?
Last Updated 2022