How to Use This Tool
Type a number and choose a style. The other conventions are shown underneath so you can see what the same number looks like written the other way.
The "and"
British English inserts and before the last part of a number: one hundred and twenty-three. American English omits it: one hundred twenty-three.
Neither is wrong and both are understood everywhere. What matters is consistency — a document that uses both looks careless in a context where care is the point. If you are writing for a specific audience, match theirs.
Billion means two different numbers
This is the one that costs money. On the short scale, used in all modern English, a billion is a thousand million. On the long scale, a billion is a million million — a thousand times larger.
Britain used the long scale officially until 1974. Much of continental Europe still does, so a document translated from French, German, Spanish or Italian may contain a "billion" that is not the number an English reader assumes. In anything financial or legal crossing a language boundary, write the digits alongside the words.
Cheque conventions
The cheque format is not stylistic. Each part has a purpose:
- The words are legally authoritative. If the words and the digits disagree, banks generally honour the words, because they are harder to alter convincingly.
- "Only" at the end marks where the amount stops, so nothing can be appended.
- Filling the line, historically with a drawn line through the remaining space, exists for the same reason.
- Pence as a fraction — "and 56/100" — is the American convention and is also about making the ending unambiguous.
Hyphens
Compound numbers from twenty-one to ninety-nine take a hyphen: twenty-one, forty-seven, ninety-nine. Larger numbers do not: two hundred, three thousand. This is one of the few number-writing rules that is genuinely a rule rather than a regional preference, and it is the one most often missed.
When to write words at all
Most style guides agree on roughly this: spell out numbers below ten in prose, use digits from ten up, and never start a sentence with a digit. Technical and scientific writing uses digits throughout, because comparability matters more than flow. Legal and financial writing uses both together, so that each checks the other.