Writing numbers can be tricky, especially because there are conflicting rules about how to do it. The Associated Press, for example, has different guidelines than other popular style manuals.  And everybody’s rules seem to have complicated exceptions.

In general, as with most writing rules, I recommend using common sense, simplicity and consistency. Keeping in mind that your firm’s style guide (you should have one, remember?) may differ, here are a few basic tips related to numbers.

Spell out numbers below 10 and big round numbers.
Nine, 15, one thousand

If you chose to spell out multi-word whole numbers between 22 and 99, use hyphens.
Twenty-three

Also use hyphens when those numbers are part of bigger numbers.
seven thousand two hundred and twenty-four

When writing large numerals, use commas. Count three spaces to the left of the ones column and continue to do so as the numbers get bigger.
1,294
2,385,482

Sometimes the most readable format is a combination of numerals and words.
600 million

Spell out simple fractions, such as 1/2 or 1/3, using a hyphen.
Two-thirds

For complicated fractions, it might be preferable to use numerals or to convert to decimals.
Six-thirteenths or 0.46

With decimals, it’s helpful to put the zero before the decimal unless the decimal itself begins with a zero.
0.715
.097

Avoid mixing fractions and decimals – or numerals and words – in the same document, if possible.
Wrong: On eBay, a collectible can cost anywhere from $5 to five million dollars.
Better: On eBay, a collectible can cost anywhere from $5 to $5 million.

Reword sentences to avoid starting with a numeral (or spell it out).
Wrong: 7,000 tickets were sold in the first hour.
Better: Concert-goers bought 7,000 tickets in the first hour. OR Seven thousand tickets were sold in the first hour.

Similarly, avoid placing two numerals back to back.
Wrong: 9 12-year-olds
Better: nine 12-year-olds

About the Author:

Erin Leslie Gordon is a freelance legal affairs journalist and a former staff writer at The Daily Journal. A “recovering” lawyer, she also spent five years as an adjunct professor teaching writing at UC Hastings College of the Law.