Ordinal Numbers: Definition, Formation Rules, and How They Differ from Cardinal Numbers

Numbers do two different jobs in everyday English. When you’re counting, you reach for cardinal numbers (two apples, twenty-nine pages); when you’re putting something in order, you reach for ordinal numbers (the second apple, the twenty-ninth day). Anyone studying number sets meets both families early on, using the same set of numbers to count in one context and to rank in another.

Cardinal numbers

Cardinal numbers match the counting sequence and answer “how many”: two, twenty-nine, one hundred and four. In English they don’t change form for gender, unlike in some other languages — “two apples” and “two oranges” use the same word “two” regardless of what’s being counted.

Example: on a shopping list, “three apples, two oranges, one bottle” are all cardinal numbers: they count items, they don’t put them in order.

Ordinal numbers

Ordinal numbers show the position of something or someone in an ordered sequence: first, second, third. Most of them are formed by taking the cardinal number and adding the suffix -th: four becomes fourth, six becomes sixth, ten becomes tenth.

Seven ordinals break that pattern. Three have no connection at all to their cardinal form: first, second and third. Four more keep the -th suffix but shift their spelling: five becomes fifth, eight becomes eighth, nine becomes ninth, and twelve becomes twelfth. Every other ordinal simply adds -th to the cardinal, sometimes dropping a final letter, as in twenty becoming twentieth.

Cardinal	Ordinal	Cardinal	Ordinal
one	1st, first	eleven	11th, eleventh
two	2nd, second	twelve	12th, twelfth
three	3rd, third	thirteen	13th, thirteenth
four	4th, fourth	fourteen	14th, fourteenth
five	5th, fifth	fifteen	15th, fifteenth
six	6th, sixth	sixteen	16th, sixteenth
seven	7th, seventh	seventeen	17th, seventeenth
eight	8th, eighth	eighteen	18th, eighteenth
nine	9th, ninth	nineteen	19th, nineteenth
ten	10th, tenth	twenty	20th, twentieth

The same rule carries on past twenty, with the tens taking -ieth in place of a final -y: thirty becomes 30th (thirtieth), forty becomes 40th (fortieth), and so on up to ninety becoming 90th (ninetieth), with one hundred becoming 100th (hundredth). Compound numbers only change their last word: seventy-one becomes 71st (seventy-first), and one hundred ninety-eight becomes 198th (one hundred ninety-eighth).

How ordinals are written in figures

Ordinals are usually written as a number followed by a suffix that depends on the last digit: -st for numbers ending in 1 (21st, 31st), -nd for numbers ending in 2 (22nd, 32nd), -rd for numbers ending in 3 (23rd, 33rd), and -th for everything else, including all the multiples of ten (20th, 30th). From 11 to 19 the rule is overridden: the suffix is always -th, so 11th, 12th and 13th never take -st, -nd or -rd even though their last digit would suggest it.

Style guides differ on when to spell an ordinal out versus using figures — AP style spells out first to ninth and switches to figures from 10th, while the Chicago Manual of Style spells out up to one hundredth — so treat “spell it out for small numbers” as a common convention, not a fixed rule.

Where the ordinal goes in a sentence

Ordinals usually come before the noun they describe: the third chapter, the second door. Royal and papal names flip that order: the ordinal follows the name and is written almost always as a roman numeral, as in Henry VIII or John Paul II. In writing, the numeral stays in roman numerals; read aloud, it becomes an ordinal — Henry VIII is spoken as “Henry the Eighth”, not “Henry the Eight”.

Example: on a date written as “the third of July”, the day takes the ordinal form; written as a bare figure, “July 4”, the ordinal is skipped.

Cardinal and ordinal numbers side by side

Put the two side by side and the distinction is simple: a cardinal number answers “how many” and stays fixed to a quantity, while an ordinal number answers “which one” and depends on a sequence. “Four books” is a cardinal number and a cardinal number meaning of quantity; “the fourth book” is an ordinal number describing where that book sits on the shelf. Cardinal and ordinal numbers share the same numerals — four and fourth both trace back to “4” — though each fills a different grammatical role in a sentence.

Anyone reviewing counting and sequencing also runs into ordinals and cardinals in arithmetic, where they help read sequences and progressions, and in algebra, where a formula referring to “the nth term” of a sequence uses a generic ordinal to stand in for all the others.