Ordinal Number Converter
An ordinal number indicates position or rank in a sequence. In English, ordinals are formed by adding a suffix to the cardinal number: 1st, 2nd, 3rd, 4th, and so on. The rule has one important exception: numbers ending in 11, 12, or 13 always use "th" regardless of the last digit. This converter accepts any positive integer and returns the correct ordinal form with its numeric abbreviation (1st, 22nd, 113th) as well as the written-out ordinal word form for numbers up to one trillion.
Ordinal suffix rule
if (n % 100 in [11,12,13]) suffix = "th" else if (n % 10 == 1) suffix = "st" else if (n % 10 == 2) suffix = "nd" else if (n % 10 == 3) suffix = "rd" else suffix = "th"
The last two digits determine the suffix. Numbers 11, 12, and 13 always use "th" because of the "th" pronunciation of the "teens". This applies equally to 111, 112, 113, 1011, 1012, etc.
Ordinal suffix examples
- 1st, 21st, 31st, 101st: End in 1 (but not 11).
- 2nd, 22nd, 32nd, 102nd: End in 2 (but not 12).
- 3rd, 23rd, 33rd, 103rd: End in 3 (but not 13).
- 11th, 12th, 13th, 111th, 112th, 113th: Always "th" (exception rule).
- 4th through 10th, 14th through 20th, etc.: All use "th".
Ordinal number converter: frequently asked questions
What is an ordinal number?
An ordinal number expresses rank or position in a sequence. Examples: 1st (first), 2nd (second), 3rd (third), 4th (fourth). Cardinal numbers (1, 2, 3) count quantity; ordinal numbers (1st, 2nd, 3rd) indicate position.
Why do 11th, 12th, and 13th end in 'th' instead of 'st', 'nd', 'rd'?
The suffixes st, nd, rd apply when the last two digits are NOT 11, 12, or 13. Numbers ending in 11, 12, 13 always use 'th' because they are exceptions in English. So 111th, 211th, and 1011th all use 'th', while 21st, 31st, and 101st use 'st'.
What is the rule for ordinal suffixes in English?
If the last two digits are 11, 12, or 13: use 'th'. Otherwise: if last digit is 1, use 'st'; if last digit is 2, use 'nd'; if last digit is 3, use 'rd'; all other last digits use 'th'. Examples: 1st, 2nd, 3rd, 4th, 11th, 12th, 13th, 21st, 22nd, 23rd.
What is the largest number that follows the exception rule?
The exception applies to any number whose last two digits are 11, 12, or 13: so 11th, 12th, 13th, 111th, 112th, 113th, 211th, and so on up to any arbitrarily large number. The rule applies based purely on the last two digits.
Are ordinal numbers used in everyday writing?
Yes. Ordinals appear in dates (June 15th), rankings (1st place), floor numbers (3rd floor), edition numbers (4th edition), and numbered lists. In formal writing, some style guides spell out small ordinals (first, second, third) rather than using abbreviations.
Official sources
- NIST SP 811 (Appendix B): Number expression conventions in US scientific writing.
- Chicago Manual of Style: ordinal number conventions referenced in NIST writing guides.
Reviewed by the CalculatorHub team, edited by James Graham, 15 June 2026. See our methodology.