Cardinal vs Ordinal Numbers: What's the Difference?
Last updated 24 August 2026
Cardinal numbers answer “how many” — one, two, three. Ordinal numbers answer “in what position” — first, second, third. Choosing the right form keeps dates, rankings, and lists clear.
Cardinal numbers
Cardinals count quantity: three apples, forty guests. They are the default form our converter produces.
A cardinal answers a question about size, and it behaves like a quantity in a sentence: it can be added to, compared, and pluralised with the noun it counts. Forty guests and forty-one guests differ by exactly one guest. This is the form used for money, measurements, counts and totals — and the form written on a check, because a check states an amount rather than a position.
Ordinal numbers
Ordinals mark order: first place, the 21st century. In words they usually end in -th, with the irregulars first, second, third, fifth, eighth, ninth, twelfth. Compound ordinals hyphenate like cardinals: twenty-first, forty-third.
An ordinal answers a question about rank, and it does not behave like a quantity: you cannot add third to fourth. It also takes the definite article far more often — the third attempt, not a third attempt, unless you mean one more in a series.
Quick reference
| Number | Cardinal | Ordinal |
|---|---|---|
| 1 | one | first |
| 2 | two | second |
| 3 | three | third |
| 5 | five | fifth |
| 12 | twelve | twelfth |
| 20 | twenty | twentieth |
| 21 | twenty-one | twenty-first |
| 100 | one hundred | one hundredth |
| 101 | one hundred one | one hundred first |
The last two rows are worth reading twice. One hundredth is 100th; one hundred first is 101st. Dropping a word changes the number by one.
Forming the ordinal
Most ordinals are the cardinal plus -th. Three patterns cover the rest:
- Irregulars: one/first, two/second, three/third, five/fifth, eight/eighth, nine/ninth, twelve/twelfth.
- Tens in -y become -ieth: twenty → twentieth, forty → fortieth.
- Compounds change only their last element: twenty-one → twenty-first, forty-two → forty-second. Never suffix the whole compound — forty-twoth is not a word.
A third kind: nominal numbers
Some numbers count nothing and order nothing. A bus route, a jersey number, a telephone number and a postcode are labels that happen to be written with digits. They are read as digit sequences rather than as quantities — route four-oh-one, not route four hundred one — and they are never spelled out in words. Recognising this category avoids a common awkwardness in formal writing, where a house style that says “spell out numbers under one hundred” would otherwise produce Room twelve for what everyone calls Room 12.
When each form appears
- Dates: ordinals in speech and in formal invitations (the first of May), figures in most written dates (1 May, May 1).
- Rankings and sequences: ordinals — finished forty-second, the third quarter.
- Amounts and counts: cardinals — forty-two dollars, three hundred pages.
- Centuries and anniversaries: ordinals, either spelled or with a suffix — the twenty-first century, her 40th birthday.
Figure forms
Ordinals also have a short form: the figure plus the last two letters of the written word — 1st, 2nd, 3rd, 4th. The suffix follows the final digit, so 21st, 22nd and 23rd behave like 1st, 2nd and 3rd, while the teens are the exception and all take -th: 11th, 12th, 13th. Write them lowercase and unsuperscripted, and without an apostrophe: the 1990s, not the 1990’s.
Related
- How to spell numbers in words covers the cardinal side in full.
- Writing numbers in legal documents explains where each form belongs in formal drafting.
Every number page on this site lists both forms — for example, 21 in words.