The UK Rules

Rules for Writing Numbers

Authors and professional writers can count on these tips to figure out the written rules of using a large number or a numeral.

SPELLING NUMBERS AS WORDS: We list the key guidelines for writing numbers and rules for numerals.

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.

For example, should you write the positive integer '5' as a figure? Or, do formal writing ethics dictate that it would be better to write the number 'five' spelled out as a word?

Writing Rules for Numbers

There are some basic rules to follow when you express arithmetical values in business letters, essays, and 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?

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

As a rule, 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.

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

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 which get used to express the concept of 'three-ness'.

Writing Numbers Rules

Always use numerals:

When to Use a Comma

In written English, we use the comma to separate thousands and as the period separator in decimals. The 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 should be expressed as 243,610 square kilometers (or 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, they should get spelled out. Thus, during the 'Seventies' or in the 'twentieth century' - for example.

Percentages and Food Recipes

You can use some digits with informal everyday writing. So, jotting a recipe as 'mix 3 cups of jasmine rice' is fine. But, you should spell the percentage out like 'eight percent of the population' in formal communication.

Expressing a percentage such as '8% of the population' should only get written for visual presentation - such as in business use.

Rounding Numbers and Estimations

Tip: Spell out estimations! The simplest rule applies to numbers rounded up or estimated - use spellings. Those rounded higher than one million should get written as a numeral plus a word. Thus, write 'around 300 million people' instead of 'around 300,000,000 people'. Exact numbers should always get written out.

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'. 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 '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. Spell it out when used in a quote such as '…four score..' and not '…4 score..'

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

Rules for Writing Numbers and Numerals in Written English