Ordinal numbers: Definition, examples, and how to use them

Mik aka NatureCrankByMik aka NatureCrank Updated on
A colorful cartoon caterpillar on a green hill with circles showing 1st, 4th, 6th, 8th, and 10th, with birds holding banners for First, Second, and Third.
Using a caterpillar and birds to visualize the order of ordinal numbers.
Hey there! Quick note: As an Amazon Associate, I earn from qualifying purchases through affiliate links in this post—at no extra cost to you. Your support helps fuel my passion for sharing great content—thanks a bunch!

Coming in first place or celebrating a 21st birthday are everyday moments where we rely on ordinal numbers. Unlike cardinal numbers that count ‘how many,’ ordinals define a specific position in a sequence. From race results (1st place) to anniversary dates (the 25th), these numbers provide the necessary context for order and rank.

Quick summary of ordinal numbers

  • Definition: Numbers that show rank or position (1st, 2nd, 3rd).
  • The suffix rule: Most end in -th, except those ending in 1 (-st), 2 (-nd), or 3 (-rd).
  • The teen exception: 11th, 12th, and 13th always end in -th.

What are ordinal numbers?

An ordinal number indicates a specific place in a defined order. While we use them daily to keep schedules and rankings in order, the mathematical theory behind them was formalized by Georg Cantor in the 1800s. He used ordinals to describe ‘well-ordered sets’—a concept that remains the foundation for how we organize everything from alphabetized lists to computer code today.

In daily life, we use these numbers to organize information. For example, in the sequence A, B, C, D:

  • A is the 1st (first) letter.
  • B is the 2nd (second) letter.
  • C is the 3rd (third) letter.

Cardinal vs. ordinal numbers: Key differences

Knowing the difference helps avoid common grammar slips.

FeatureCardinal numbersOrdinal numbers
Primary purposeCounting and quantityRanking and position
Question answeredHow many?Which one?
Examples1, 5, 20, 1001st, 5th, 20th, 100th
Usage“I have three cats.”“This is my third cat.”

How to write ordinal numbers and suffixes

Writing ordinal numbers involves adding a specific suffix to the end of a cardinal number. There are four primary suffixes in English: -st, -nd, -rd, and -th.

The “th” rule and exceptions

Most ordinal numbers end in -th (4th, 10th, 100th). However, the first three numbers in every ten (except for the teens) have unique endings:

  • Numbers ending in 1 use -st (1st, 21st, 31st).
  • Numbers ending in 2 use -nd (2nd, 22nd, 32nd).
  • Numbers ending in 3 use -rd (3rd, 23rd, 33rd).
  • The “teen” exception: 11, 12, and 13 always use -th (11th, 12th, 13th). Unlike other numbers ending in 1, 2, or 3, the “teens” do not change their suffix because they are pronounced as unique words (eleventh, twelfth, thirteenth) rather than compound words like “twenty-first.”
A comparison chart showing the difference between standard ordinal suffixes like 21st and 22nd versus the teen exceptions 12th and 13th.
Pro tip: Don’t let the ‘1, 2, 3’ at the end of 11, 12, and 13 fool you—they always end in -th!

Important: Remember that for the entire group from 11 to 19, you will always use the -th suffix.

Ordinal numbers chart: 1 to 100

CardinalOrdinal (numeral)Ordinal (word)
11stFirst
22ndSecond
33rdThird
44thFourth
55thFifth (v changes to f)
99thNinth (drop the e)
1010thTenth
1111thEleventh
1212thTwelfth (v changes to f)
2020thTwentieth (y changes to ie)
2121stTwenty-first
3030thThirtieth
4040thFortieth (no “u” in forty)
100100thOne hundredth

Frequently asked questions about ordinal numbers

Ever tried to ask a question and realized there isn’t a word for ‘what number-eth’? You aren’t alone. English lacks a dedicated ordinal question word, so we usually say:

  • “What place did you finish in?”
  • “Which president was Abraham Lincoln?”
  • “In what order do these files go?”

The “teen” numbers (11–19) always use the -th suffix. The rule for -st, -nd, and -rd only applies when the number 1, 2, or 3 is the final digit of a compound number. Because 11, 12, and 13 are not compound numbers (we don’t say “ten-one”), they don’t take the individual suffixes.

In spoken English, we almost always use ordinals for dates (e.g., “July fourth”). However, in modern written English, it is standard to use cardinal numbers: July 4 or 4 July. You should only use the ordinal suffix (July 4th) in very informal writing, or if the month is omitted and you are referring to the day specifically (e.g., “The party is on the 4th”).

In standard language, no. However, in computer science and mathematics, “zeroth” (0th) is used to describe the very first element in an array or a sequence that starts at zero. This is called “zero-based indexing.”

Centuries always use ordinal numbers. While general style guides suggest spelling out numbers under ten, the 1st century and 2nd century are frequently written as numerals in historical and web content to improve readability.

Conclusion: Mastering the order of things

Ordinal numbers are more than just suffixes like -st or -th; they are the framework we use to organize our world, from historical centuries to the dates on our calendars. By understanding the simple rules for suffixes and the “teen” exceptions, you can ensure your writing is both grammatically correct and easy to follow.

Whether you are teaching a student about cardinal vs. ordinal numbers or just double-checking the spelling of “fortieth,” we hope this guide cleared up the confusion.

Join the conversation

Did you find the “zeroth” rule surprising, or do you have a trick for remembering the 11th, 12th, and 13th exception? Leave a comment below and let us know which part of ordinal numbers usually trips you up!

If you found this guide helpful, please share it with a friend or colleague who might be brushing up on their grammar. Your shares help us create more free resources like this one.

Discover more from English Learning Tips

Subscribe to get the latest posts sent to your email.

Mik aka NatureCrank

About the author
Mik is a veteran, educator, and writer who has lived off-grid and nomadic since 2020. His perspective is shaped by a diverse career in both for-profit and non-profit management, as well as years of experience as an instructor in biology, psychology, health, and ESL.

By blending his formal studies in counseling and science with the practical realities of life on the trail, Mik provides a unique, grounded approach to nature-based healing. When he isn’t documenting the natural world through wildlife photography and geology, he is exploring the intersection of scientific research and the restorative power of the outdoors.

Leave a replay but be nice!