How to Spell Numbers in Words (Complete Rules)
Last updated 24 August 2026
Spelling a number in words follows a small set of consistent rules. The short answer: write the number from the largest group down, hyphenate two-word numbers from twenty-one to ninety-nine, and group thousands, millions, and billions.
The core rules
- 0–20 are unique words: zero, one, two … twenty. There is nothing to derive here; they are simply learned.
- Tens are twenty, thirty … ninety. Combine with a hyphen: twenty-one, sixty-seven.
- Hundreds read as “[digit] hundred”, e.g. three hundred. Add the rest after: three hundred forty-five.
- Groups of three (thousand, million, billion) are read left to right: 12,500 → twelve thousand five hundred.
How the grouping actually works
Long numbers are less about memorising forms than about splitting correctly. Take the digits in threes from the right, name each group exactly as you would name a three-digit number, and append that group’s scale word:
1,234,567 → 1 | 234 | 567 → one million, two hundred thirty-four thousand, five hundred sixty-seven
A group of all zeros contributes nothing at all. That is why 1,000,000 is one million and not one million zero thousand zero — and it is the single insight that makes very large numbers easy rather than intimidating.
The irregular teens
Between ten and nineteen, English does not build compounds. Fifteen is one irregular word, not ten five; thirteen is not ten three. This trips up learners and it also explains a quirk of the hyphen rule: there is no hyphen in the teens because there is nothing to join. The compounds only start at twenty-one.
Hyphens
Hyphenate every compound from twenty-one to ninety-nine, and nothing else. Not between a digit word and hundred (four hundred, never four-hundred), and not before a scale word (two thousand, not two-thousand). In a long number, each group of three contributes at most one hyphen, and fractions take their own hyphen between numerator and denominator: two-thirds, three-quarters.
British vs American “and”
British English inserts and before the final tens/units: one thousand and five. American English usually drops it: one thousand five. Both are widely understood; be consistent within a document. The “and” never appears when the number has no tens-or-units part, which is why one thousand five hundred is identical in both. A separate “and” appears on a cheque, where it separates dollars from cents rather than joining parts of the number — see the guide to writing a check.
Words or digits?
Spelling is one question; whether to spell at all is another, and it is a matter of house style rather than grammar:
- Chicago spells out whole numbers from zero through one hundred, and round multiples of large numbers.
- AP spells out one through nine and uses figures from 10 up, with exceptions for ages, percentages and money.
- Most scientific and technical styles use figures for anything measured, and words only where a figure would start a sentence.
Two conventions are near-universal whatever guide you follow: do not begin a sentence with a figure (recast the sentence instead), and do not mix forms for comparable values in one passage — between 5 and 20 people, not between five and 20 people.
Common mistakes
- Forgetting the hyphen (writing “twenty one” instead of “twenty-one”).
- Adding “and” in the wrong place in American style.
- Mixing digits and words for the same value in formal writing.
- Writing one hundredth when you mean 101st (one hundred first).
- Assuming billion is unambiguous — modern English uses the short scale, but older British texts and several European languages do not.
See the Chicago Manual of Style and AP Stylebook for house-style guidance on when to spell numbers out versus use digits.
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