Cardinal and ordinal numbers

The two kinds

A cardinal number answers “how many”: one, two, three, ninety, one thousand. An ordinal answers “which one in order”: first, second, third, ninetieth, one thousandth.

There is a third kind you meet less often. A nominal number is a label: a bus route, a jersey number, a room. Nothing is counted or ordered by it, and it is always written in digits.

How an ordinal is built

Take the cardinal and change its last word. That is the entire rule, and it holds however long the number is.

• twenty-one becomes twenty-first
• one hundred and five becomes one hundred and fifth
• one million becomes one millionth

Only the last word changes. Everything in front of it stays as it was.

The seven irregular ones

Most ordinals are the cardinal with “th” added. These seven change shape, and they are the ones that turn up misspelled.

Three of them lose or change a letter as well: five becomes fifth, twelve becomes twelfth, and nine drops its e in ninth. Eight adds only an h, giving eighth with a single t.

The tens change a letter too, all by the same rule: the y becomes ie before the th, so twenty becomes twentieth and ninety becomes ninetieth.

The short form, and the teens trap

Written with digits, an ordinal takes the last two letters of its word: 1st, 2nd, 3rd, 4th. The exception is the teens, which all take “th” whatever their last digit: 11th, 12th and 13th, not 11st, 12nd and 13rd. That carries through to every hundred, so 111th and 112th follow the teens as well.

A note on superscripts

Raising the suffix, as in 1^st, is a matter of typographic preference. Most modern style guides advise against it because it breaks the line spacing and does not survive being copied between programs. Dates written in the international order, 2026-09-20, take no suffix at all.