If you work on reports, presentations, or any other kind of formal writing, you need to know the right way to handle numbers in written documents. In this post, we offer some useful tips on formatting numbers in formal writing, to help you avoid common mistakes.
Words, Digits, or a Mixture of Both?
If you’re following a style guide, it might include instructions about whether to use words or digits when writing numbers. If no style guide is provided, the general rule is to write numbers up to nine using words and higher numbers with Arabic numerals:
We expect to launch five new products this year.
We received 28 applications for the Sales Manager position.
Sometimes, it’s easier to read large numbers when they’re written with a mixture of words and digits like this:
The human body is made up of an estimated 37.2 trillion cells.
Most people would agree that this is much easier to understand than 37,200,000,000,000!
But, what if the scientists were more accurate and told us that the human body contains exactly 37,236,430,000,000 cells? You might expect to write this as 37.236430 trillion. While that would be the correct number, it would be better to simplify it to 37.24 trillion, because large numbers should generally be written to a maximum of two decimal places.
Percent or %?
When writing percentages, the convention is to use “%” after numerals and “percent” (or “per cent” in UK English) after numbers written in words:
The average electricity bill went up by 15% last year.
We’re offering a five percent discount on woolly hats.
There are exceptions to this guidance though, so always consult your style guide (if you have one) for the last word.
One common mistake our proofreaders come across is using percentages in connection with a small number of results. When you present figures about small groups, you should use a different way to describe them. So for example, if eight people had completed a questionnaire, rather than writing “87.5% of respondents preferred the red hats,” it would be better to say “seven out of eight respondents…”
How to Punctuate Math Symbols
Math symbols (e.g., +, -, x, and =) usually have a space on either side:
2 + 2 = 4
48 x 19 = 912
However, if you’re using “–” to indicate a negative value, it doesn’t need a space after it:
Ice cream should be stored at -18°C.
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Other notable exceptions are the “%” sign, which always comes directly after the digits, and the division slash “/”, which – unlike other operators – doesn’t require spaces either side:
Shockingly, 88% of statistics are made up on the spot.
Studies have shown that 3/10 adults sleep with a cuddly toy.
Always Use a Period to Indicate a Decimal Point
When writing decimals or currency, you should always use a period (or full stop) to indicate the decimal separator:
Americans eat 4.25 billion avocados each year. ✔
The world record for solving a Rubik’s cube is 3,47 seconds. ✘
Avoid Starting a Sentence with a Numeral
It is usually incorrect to start a sentence with a numeral:
300 donuts should be enough. ✘
You should either replace the numerals with words, or avoid the issue by rewording the sentence:
Three hundred donuts should be enough. ✔
There should be enough donuts if we get 300. ✔
Punctuate Numbers Consistently
When you write long numbers, it is normal (although not compulsory) to punctuate them by placing a comma every third digit from right to left:
There are 75,600 calories in 300 donuts.
Walking 2,003,400 steps will burn 75,600 calories.
As we mentioned, this kind of punctuation isn’t mandatory, unless your style guide says so. The most important thing, therefore, is to be consistent.
Free Proofreading Trial
We hope these tips have cleared up any issues you’ve had with numbers in your writing. If you’d like an expert to check your work for errors – including mistakes in formatting statistics, and so on – our proofreaders are available 24/7. You can even try our service for free by submitting a 500-word document today.