The rules that get broken most
Writing a number out looks mechanical until one of these four turns up, and these are the ones you see written wrongly every day:
- The hyphen. Every compound from twenty-one to ninety-nine takes one: twenty-one, forty-five, ninety-nine. Hundreds and thousands do not.
- Forty has no u. Four, fourteen and fourth keep it; forty drops it. It is the single most common misspelling in written-out numbers.
- The «and» is British. One hundred and one on this side of the Atlantic, one hundred one on the other. Neither is wrong, but mixing them within one document is.
- No plural on the scale words. Two hundred, three thousand, five million — never «two hundreds». They only take an s when they are vague: hundreds of people.
Writing an amount on a cheque
On a cheque the amount appears twice, in figures and in words, and if they disagree the words win. That is why the usual form puts the pence as a fraction: ONE HUNDRED AND TWENTY POUNDS AND 50/100. Writing it that way, in capitals, stops anyone adding digits after the amount — which is exactly what the double entry protects against.
The currency goes in the plural unless the amount is one, and this page uses the currency of the country selected above, with its own fraction: pence for pounds, cents for dollars and euros, paise for rupees.
A billion is not the same everywhere
English uses the short scale: a billion is a thousand million, a one followed by nine zeros. Spanish, French and German use the long scale, where the equivalent word means a million million — a thousand times more. Translating the word instead of the number multiplies or divides the figure by a thousand.
Britain officially switched to the short scale in 1974, which is recent enough that older British documents can still mean the long-scale value. When a figure comes from an old source, it is worth checking which scale it was written in before quoting it.
What is worth knowing
Numbers written out take no thousands separators: they run as they are spoken. And in formal documents it is better not to split a number across two lines — if it does not fit whole, move it to the next one.
This page writes up to 999,999,999,999,999, the largest number a browser handles without losing the last digit. Beyond that the figures stop being exact, and writing out a number that has already been rounded would give it an appearance of precision it does not have.