Sometimes it can be confusing to know how to correctly write numbers. For example, when do you use digits (figures - 1, 2, 3, etc.) and when do you use words (letters - one, two, three, etc.)?

One - Numerals and numbers:

Firstly, we should look at the difference between numerals and numbers. It's pretty simple really - a number is a non-figurative concept while a numeral is a symbol that is used to express the concept. So, "4", "IV" and "Four" are all numerals (symbols) that express the same number (or, rather, the idea of the number four).

Two - Always spell out small numbers:

Whole numbers that are smaller than eleven should be spelled out in words. This is a constant rule, especially in more formal writing. So, in letters and documents, write "nine" instead of "9".

Three - There are no other constant rules:

There is a lot of disagreement among experts about the rules. Some say that any one-word number should always be written out in words, others say that two-word numbers should be written out in figures. So, you should write out "eleven" or "ninety" but not "23".

Four - Use of the comma:

In English, the comma is used to separate the thousands from the hundreds and tens (as in 2,000,500 or 1, 349 for example). This is to make larger numbers easier to read. A full stop (.) is used as the decimal point (as in 7.980). In continental Europe the opposite is the case, whereby full stops are used to separate whole, large numbers and the comma is used as the decimal point ( for example, 5.000 and 7,980).

Five - Never start a sentence with a numeral:

You should never start a sentence with a numeral, as in "4 men went to sea" - it should be "Four men went to sea". For large numbers, this might be difficult, so it is best to rewrite the sentence so the numeral is not the first word: "A lucky winner scooped $90,000 in the lottery" instead of "Ninety thousand dollars was scooped by a lucky lottery winner".

Six - Always spell out centuries and decades (unless stated otherwise):

Use "twentieth century" or "the Nineties", unless the type of document you are writing stipulates that you write "19th century" or "1990s".

Seven - Two numbers next to each other:

It can be confusing and difficult to read "100 10-year-olds", so it is far better to write one of them as a numeral: "100 ten-year-olds". Choose the number that has the fewest letters.

Eight - Recipes and percentages:

Here, you can use digits, such as "17% of women prefer cats to men" or "add 3 cups of flour". In more formal writing, however, you may prefer to spell out the percentage sign: "17 percent of women prefer cats to men".

Nine - Rounded numbers or estimates:

Any rounded numbers over a million are written out as a numeral: "Approximately 900 million people are learning English". This is easier to read than writing "900,000,000". However, if you are writing an exact number, you must write it out in full (900,598,984).

Ten - Ordinal numbers

We often use ordinal numbers for dates or competitions: "The first of May", "She came second in the race" etc. In dates, you can write the number out as a figure: "2nd June" but you would never write "It was my 1s t job". Instead, it is correct to write "It was my first job."

It is important to be consistent in your writing when using numbers, so bear this in mind as otherwise your work can seem unprofessional and difficult to understand.

KJ Hutchings is the founder of KJ Language Services, offering editing, writing and proofreading services and advice on how you can make your English language documents the very best they can be. For more information, visit http://www.kjlanguageservices.com/