What is the difference between cardinal and ordinal numbers?

Cardinal numbers count quantity (one, two, three) while ordinal numbers show position or order (first, second, third).

How do you spell 1st, 2nd and 3rd?

First, second and third. These three are irregular; from fourth onward most ordinals simply add -th.

Reference · Order & position

Ordinal Numbers in Words

Q: How do you write 21st in words?

Twenty-first. Only the last word becomes ordinal, so twenty stays and one becomes first.

Updated: June 2026

Ordinal numbers tell you where something sits in a sequence — first, second, third — rather than how many there are. They follow a tidy pattern once you’ve learned the three irregular forms, and this page lays out the full chart plus the rules for building any ordinal you need.

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Cardinal vs ordinal

A cardinal number answers “how many?” — one apple, three chairs, fifty people. An ordinal number answers “in what position?” — the first apple, the third chair, the fiftieth person. In writing, ordinals appear as words (first, second) or as a digit with a two-letter suffix (1st, 2nd). The suffix matches the sound of the word: st for first, nd for second, rd for third, and th for almost everything else.

How ordinals are formed

Three ordinals are irregular and must be learned: first, second and third. After that the system is regular with a few spelling shifts:

Most numbers add -th: four → fourth, six → sixth, ten → tenth.
Five and twelve change to fifth and twelfth; nine drops its e to make ninth; eight adds just an h for eighth.
The tens swap their final -y for -ieth: twenty → twentieth, forty → fortieth, ninety → ninetieth.
In compound numbers, only the last word becomes ordinal: twenty-one → twenty-first, one hundred → one hundredth, two thousand five → two thousand fifth.

Chart: 1st to 31st

#	Ordinal	#	Ordinal
1st	first	17th	seventeenth
2nd	second	18th	eighteenth
3rd	third	19th	nineteenth
4th	fourth	20th	twentieth
5th	fifth	21st	twenty-first
6th	sixth	22nd	twenty-second
7th	seventh	23rd	twenty-third
8th	eighth	24th	twenty-fourth
9th	ninth	25th	twenty-fifth
10th	tenth	26th	twenty-sixth
11th	eleventh	27th	twenty-seventh
12th	twelfth	28th	twenty-eighth
13th	thirteenth	29th	twenty-ninth
14th	fourteenth	30th	thirtieth
15th	fifteenth	31st	thirty-first
16th	sixteenth	40th	fortieth

Where ordinals appear

Ordinals are everywhere: dates (the third of May), floors (the twelfth floor), monarchs and popes (Elizabeth the second), rankings (she finished twenty-first) and fractions, where the denominator borrows the ordinal form — a fifth, three quarters, two thirds. Switch the converter to Ordinal mode and it turns any whole number straight into its ordinal word, handling the irregular and compound cases for you.

Frequently asked questions

What is the difference between cardinal and ordinal?

Cardinals count (one, two, three); ordinals rank (first, second, third).

How do you write 21st in words?

Twenty-first — only the last word, “one”, becomes ordinal.

How do you spell 1st, 2nd, 3rd?

First, second and third — the three irregular ordinals.

What is 100th in words?

One hundredth; 1000th is one thousandth.