When should you write numbers as words?

When should you write numbers as words and when as figures?

Most people guess. But guessing leads to inconsistency, and inconsistency makes your writing look unprofessional.

BBC News has a simple rule in its style guide:

• Spell out numbers one to nine
• Use figures for 10 and above
• Always spell out numbers at the start of sentences.

So inside a sentence you'd write "three people attended" but "15 people attended." And at the start of a sentence you'd write "Twenty people left early" not "20 people left early."

Simple. Consistent. Professional.

The full style guide covers exceptions (like percentages, ages, and measurements) and you can find it here:

Here's the thing: if your organisation has a style guide for staff to follow then use it. Most organisations don't have a style guide so find yourself a good one and stick to it.

Some, including BBC News's and the Guardian's are on the web. Others, like the Economist's, are sold as books.

It doesn't matter which one you choose. What matters is consistency.

Because when your documents follow clear rules, they look polished. When they don't, they look like nobody cared enough to check.

Pick a guide and follow it. Your writing will instantly look more professional.