How to Use Ordinal Numbers in Writing

eHow
June 20, 2011

The rules for using numbers in writing can be confusing, as numbers can be expressed as numerals, words or phrases. The rule, generally, is never to begin a sentence with an Arabic numeral, and to spell out numerals from zero to nine. Ordinal numbers define something's position in a series, and can be expressed as words or digits followed by letters, for example: “first” or “1st”. The rules for ordinal numbers are similar to other numbers, with some variance.

Step 1
Spell out “first” through “ninth” when they indicate something's position in a sequence or in time. Examples are “second base,” “Fifth Amendment”and “first in line.”

Step 2
Use figures starting with “10th” when they indicate something's position in sequence or in time. Examples are “19th Amendment” and “21st century.”

Step 3
Use “1st,” “2nd,” “3rd” and so on when the sequence has been assigned in forming titles or names, as in geographic and military designations. Examples are “1st Ward,” “7th Fleet” and “1st Sgt.”

Step 4
Follow an organization's practice for proper nouns. These do not necessarily follow the standard rules. Examples are “20th Century Fox,” “Twentieth Century Limited,” and “1st National Bank of South Florida.”

References
“The Associated Press Stylebook”; numerals; 2007
Western Washington University: Associated Press Style Essentials