Correct spelling

11th

Correct spelling, explanation: 11th is the correct form because it’s eleventh, not ending with st but with th. Endings in ordinal numbers come from how the full-word form is spelled, not (or not only) based on the number that is there in numeral form. The confusion may come from the fact, that number 1 itself is first (1st) in ordinal form. However, 11st is incorrect and the correct form is 11th.

Definition of 11th:
numeral, the ordinal number between 10th and 12th
Julie was very excited about her 11th birthday party.
It was my 11th time in Spain and I want to come back for the 12th time!


Incorrect spelling

11st

Incorrect spelling, explanation: 11st is incorrect because the word eleventh doesn’t end with st but with th, and with such letters should end also the numeral form of the ordinal number. This is a rule: that first ends with st so does 1st; twenty-forth with th and so does 24th etc. This applies to all ordinal numbers, so to eleventh11th – as well. Therefore 11th is the correct form.

Incorrect spelling

11nd

Incorrect spelling

Incorrect spelling

11rd

Incorrect spelling