Ordinal Number Definition and Examples

Close-Up Of Number 5 Candle On Birthday Cake
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An ordinal number is a number that indicates position or order in relation to other numbers: first, second, third, and so on. Contrast these types of numbers with cardinal numbers (in math they're also called natural numbers and integers), those numbers that represent countable quantity. 

"Ordinal numbers do not represent quantity," notes Mark Andrew Lim, "but rather indicate rank and position, such as the fifth car, the twenty‐fourth bar, the second highest marks, and so on"
(The Handbook of Technical Analysis, 2012).

Learning Ordinals

If you are teaching ordinals to English language learners, introduce the concept by reviewing cardinal numbers. Then continue with the ordinals to contrast the concepts. Also, introduce the term last as a position vocabulary word.

Examples of Ordinals

All ordinal numbers carry a suffix: -nd, -rd, -st, or -th. Ordinal numbers can be written as words (second, third) or as numerals followed by abbreviations (2nd, 3rd).

  • first (1st)
  • second (2nd)
  • third (3rd)
  • fourth (4th)
  • fifth (5th)
  • sixth (6th)
  • seventh (7th)
  • eighth (8th)
  • ninth (9th)
  • tenth (10th)
  • eleventh (11th)
  • twelfth (12th)
  • twentieth (20th)
  • twenty-first (21st)
  • twenty-second (22nd)
  • twenty-third (23rd)
  • twenty-fourth (24th)
  • thirtieth (30th)
  • one hundredth (100th)
  • one thousandth (1,000th)
  • one millionth (1,000,000th)
  • one billionth (1,000,000,000th)

Using Ordinal Numbers and Cardinal Numbers Together

"When a cardinal number and an ordinal number modify the same noun, the ordinal number always precedes the cardinal number: The first two operations were the most difficult to watch. The second three innings were quite dull.

"In the first example, the ordinal number first precedes the cardinal number two. Both first and two are determiners. In the second example, the ordinal number second precedes the cardinal number three. Both second and three are determiners. Try reading the sentences with the ordinal and cardinal numbers reversed. They simply sound wrong."
(Michael Strumpf and Auriel Douglas, The Grammar Bible. Owl Books, 2004)

More Tips on Using Ordinal Numbers

"Spell out ordinal numbersfirst, second, third, fourth—except when quoting from another source. In the interests of saving space, they may also be expressed in numerals in notes and references. ...

"Use words for ordinal numbers in names, and for numerical street names ... :

the Third Reich

the Fourth Estate

a fifth columnist

Sixth Avenue

a Seventh-Day Adventist ...

"Use figures for ages expressed in cardinal numbers, and words for ages expressed as ordinal numbers or decades:

a girl of 15 a 33-year-old man

between her teens and twenties

in his 33rd year"

(R. M. Ritter, New Hart's Rules: The Handbook of Style for Writers and Editors. Oxford University Press, 2005)

"Do not use the ordinal (th, st, rd, nd) form of numbers when writing the complete date: January 15 is the date for the examination. However, you may use the ordinal suffixes if you use only the day: The 15th is the date for the examination. ...

"Write out ordinal numbers when they contain just one word: third prize, tenth in line, sixtieth anniversary, fifteenth birthday. Use numerals for the others: the 52nd state, the 21st Amendment."
(Val Dumond, Grammar for Grownups. HarperCollins, 1993)