How to write numbers in words

First: should it be words at all?

Most style guides agree on the shape of the rule even when they disagree on where the line sits. Small numbers are spelled out in running prose; large ones are left in digits; and technical, statistical or tabular writing uses digits throughout.

• Under ten, spell it out. This is the one nearly everybody follows. “Three reasons”, not “3 reasons”.
• Between ten and a hundred, it depends. Journalism usually switches to digits at ten. Book publishing often spells out everything up to a hundred.
• Never start a sentence with a digit. Spell it out or rewrite the sentence. “Ninety people came”, or “There were 90 people”.
• Keep a list consistent. If one item in a series needs digits, use digits for all of them, even the small ones.
• Money, dates, ages, measurements and page numbers stay in digits almost everywhere, whatever their size.

Cheques and contracts are the opposite case: there the number is written both ways, in digits and in words, so that the two check each other. Writing money out covers that.

The hyphen rule

Compound numbers from twenty-one to ninety-nine take a hyphen. That is the whole rule, and it applies wherever the compound appears, however large the number around it is.

• twenty-one, forty-two, ninety-nine
• one hundred and twenty-one
• four thousand five hundred and sixty-seven

Round tens take no hyphen (twenty, forty, ninety), and neither does anything either side of a scale word. It is two hundred, never two-hundred.

The “and” rule

British English puts and between the hundreds and whatever follows them. American English leaves it out. Both are ordinary, correct English in the places they are used.

• 105 is one hundred and five, or one hundred five
• 1,001 is one thousand and one, or one thousand one
• 1,500 is one thousand five hundred either way, because there is nothing after the hundred for the “and” to sit between

South African, Indian, Irish and Australian usage follows the British form. The difference is set out in full on British and American number formatting.

Commas in the words

A long number written out is sometimes punctuated with commas between the scale groups, in the same places the digits would take them: one thousand, one hundred and five. It is optional, more common in formal and legal writing than elsewhere, and never used immediately before the final “and”.

Zero, negatives and decimals

• Zero is zero in most writing, nought in British schools and on some forms, and “oh” only when reading digits aloud one at a time.
• Negatives are read as either “negative” or “minus”. Minus is more common in British speech, negative in American and in mathematics.
• Decimals are read digit by digit after the point: 3.14 is three point one four. More on decimals.