How is the short ordinal suffix chosen?

The suffix is -st for numbers ending in 1, -nd for 2, and -rd for 3, except in the 11-13 range which always takes -th. So 1st, 22nd, and 103rd are correct, but 11th, 12th, and 13th are exceptions.

Which ordinals are irregular?

The early ones change spelling: one to first, two to second, three to third, five to fifth, eight to eighth, nine to ninth, and twelve to twelfth. Tens like twenty become twentieth, and the tool handles all of these.

How are compound ordinals formed?

Only the last word becomes ordinal. So twenty-one becomes twenty-first, and one hundred forty-two becomes one hundred forty-second, while the earlier words stay cardinal.

How big a number can it convert?

It supports up to 15 digits, covering positions into the trillions. Numbers larger than that are rejected with a message so the output is never silently wrong.

Does it accept negative numbers or decimals?

No. Ordinals describe positions in a sequence, which are positive whole numbers, so only positive integers are accepted. Negatives and decimals are rejected.

English Ordinal Words

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Ordinal numbers describe position in a sequence — first, second, third — rather than quantity. They appear in dates, rankings, lists, legal clauses, and titles. English ordinals are mostly regular but start with several irregular forms that trip up automated conversion.

How it works

The number is first written as a cardinal (one, twenty-one, one hundred), then the final word is replaced with its ordinal form. The short suffix is chosen by the last one or two digits:

last two digits 11, 12, 13 -> "th"   (eleventh, twelfth, thirteenth)
otherwise last digit 1 -> "st", 2 -> "nd", 3 -> "rd", else "th"
word form: only the FINAL word changes
  five -> fifth, eight -> eighth, twenty -> twentieth, two -> second

So 42 produces the short form “42nd” and the word form “forty-second”, changing only “two” to “second” while “forty” stays as written.

Tips and example

The number 21 gives “21st” and “twenty-first”; 113 gives “113th” and “one hundred thirteenth”; 1,000,000 gives “1000000th” and “one millionth”. Use the short form in running text and dates where space matters, and the spelled-out form for formal documents, chapter headings, and anniversaries such as “the fiftieth anniversary”. Remember the 11-13 exception: although they end in 1, 2, and 3, they all take “th”.