Correct spelling

63rd

Correct spelling, explanation: this form is correct because suffix rd is connected to ordinal number third (3rd), so also to any other number ending with 3rd, like 63rd. For the same reason 63th is incorrect, because th is used for different numbers (it is a popular suffix, but it isn’t used for number 3). Therefore 63rd is the correct form.

Definition of 63rd:
numeral, ordinal number between 62nd and 64th
It’s Jerry’s 63rd birthday next week, are we having a party?
On 63rd anniversary of this battle there was a parade in the town.


Incorrect spelling

63th

Incorrect spelling, explanation: 63th is an incorrect spelling because th ending is used for those ordinal numbers which end with this sound in their full-word forms. Sixty-third (63rd) is pronounced and written with rd ending so this ending is used for number form. Therefore 63rd is the correct form.

Incorrect spelling

63st

Incorrect spelling

Incorrect spelling

63nd

Incorrect spelling