Ordinal Numbers

Overview

Ordinal numbers (first, second, third…) express position or order in a sequence — they answer the question "which one in a series?" They are formed from cardinal numbers and are used for dates, floors, rankings, centuries, and sequences.

1. Formation Rules

Most ordinal numbers are formed by adding -th to the cardinal number.

Cardinal	Ordinal	Cardinal	Ordinal
four	fourth	eleven	eleventh
six	sixth	twelve	twelfth
seven	seventh	thirteen	thirteenth
ten	tenth	twenty	twentyth

2. The Irregular First Three

The first three ordinals are completely irregular — they must be memorised.

Cardinal	Ordinal	Abbreviation
one	first	1st
two	second	2nd
three	third	3rd

3. Spelling Changes for Some Ordinals

Cardinal	Ordinal	Change
five	fifth	five → fif
eight	eighth	eight → eigh (drop -t before -th)
nine	ninth	nine → nin (drop -e)
twelve	twelfth	twelve → twelf
twenty	twentieth	twenty → twentie (y → ie)
thirty	thirtieth	thirty → thirtie

4. Ordinals 21st and Beyond

For compound ordinals, only the last word changes to the ordinal form.

Cardinal	Ordinal	Abbreviation
twenty-one	twenty-first	21st
twenty-two	twenty-second	22nd
twenty-three	twenty-third	23rd
thirty-four	thirty-fourth	34th
one hundred	one hundredth	100th

5. Key Uses

Dates

My birthday is on the third of March / March 3rd.

The meeting is on January 21st / the twenty-first of January.

Floors of a building

The office is on the fifth floor.

She lives on the twenty-second floor.

Rankings / positions

She finished first in the race.

He came third in the competition.

Centuries

We live in the twenty-first century.

Shakespeare wrote in the sixteenth century.

Sequences / order

This is the second time I've visited.

He is the first person to arrive.

6. Ordinals with the Article "The"

Ordinal numbers almost always follow the.

She is the first student to finish.

That was the third time he was late.

February is the second month of the year.

7. Common Mistakes

Mistake	Correction	Explanation
the second floor	Correct!	✓
I live on floor five	I live on the fifth floor	Use ordinal + "the"
fiveteenth	fifteenth	five → fif + -teenth
twentyth	twentieth	twenty → twentie + -th
He came in third place	Correct!	✓
She is the one best	She is the best / the first	Use ordinal correctly

8. Abbreviations in Writing

Ordinal	Abbreviation	Used for
first	1st	1st January, 1st place
second	2nd	2nd floor, 2nd March
third	3rd	3rd prize, 3rd century
fourth–ninth	4th–9th	4th July, 8th grade
eleventh onward	11th, 12th…	21st century, 100th birthday

9. Real-World Examples

The first man on the moon landed there on July 20th, 1969.

She received second prize at the competition.

Our office is on the fifteenth floor of the building.

This is the twenty-first century — things change fast.

Summary

Formation	Rule	Example
Irregular	Must memorise	1st=first, 2nd=second, 3rd=third
Most others	Add -th	4th=fourth, 10th=tenth
-y ending	y → ieth	20th=twentieth, 30th=thirtieth
Spelling change	five/eight/nine/twelve	5th=fifth, 8th=eighth
Compound	Only last part changes	21st=twenty-first