number + (th, nd, st, rd)

Ordinals (1st, 2nd, 3rd, 4th) mark position or order. Common errors: wrong suffix (11st), stray space (4 th), missing hyphen in compound adjectives (21st-century), or using an ordinal where a cardinal belongs (23rd years old).

Quick rules to apply now

No space between numeral and suffix; use -th for 11, 12, 13; pick st/nd/rd from the final digit otherwise; hyphenate ordinal + noun when it modifies another noun; prefer spelled-out ordinals in formal running text.

No space: 4th, not 4 th.
11, 12, 13 → always -th (11th, 12th, 13th).
Last digit rule: 1→st, 2→nd, 3→rd, otherwise →th (e.g., 101st, 102nd, 103rd, 104th).
Hyphenate before a noun: a 21st-century idea; no hyphen after the noun: the 21st century.
Dates: formal U.S. text usually drops ordinals (May 5); invitations and casual text can use May 5th.

Core explanation: what ordinals do and when to use them

Ordinals show order or rank (first, second, third). Use them for positions, sequence steps, named instances, and birthdays. Use cardinals for counts, measurements, ages, and quantities.

Use ordinals: She finished 1st; Step 2; his 23rd birthday.
Use cardinals: She is 23 years old; He bought 3 apples.

Ordinal: She finished first in the race.
Cardinal: She is 23 years old. (not "23rd years old")

Grammar mechanics: which suffix to use and the 11-13 rule

Check the last two digits: if they are 11, 12, or 13, use -th. Otherwise use the final digit to choose st/nd/rd/th.

21 → 21st; 22 → 22nd; 23 → 23rd; 24 → 24th.
111 → 111th (because the last two digits are 11).

Wrong: 11st →
Right: 11th
Wrong: 113st →
Right: 113th
Usage: 102 → 102nd (last digit 2)

Spacing and punctuation: attach the suffix; date tips

Always attach the suffix directly to the number: 4th (never "4 th"). Superscripts are decorative; plain suffixes are standard in most text. For formal American dates, omit the suffix: May 5, 2020. For invitations or casual writing, May 5th is fine.

Correct: 4th (no space).
Avoid superscripts in plain text; use "st/nd/rd/th" inline.
Formal dates: May 5, 2020. Informal invites: May 5th.

Wrong: 4 th →
Right: 4th
Usage: Formal: May 5, 2020 → Informal: May 5th, 2020

Hyphenation and compound modifiers

When an ordinal + noun functions as an adjective before another noun, hyphenate: a 21st-century trend, a third-party vendor. If that reads awkwardly, spell the ordinal out or change the word order.

Before a noun: a 21st-century idea (hyphenate).
After a noun: the 21st century was different (no hyphen).
Alternative: the twenty-first century (spell out in formal prose).

Wrong: 21 st century fashion →
Right: 21st-century fashion
Rewrite (formal): the twenty-first century trends

Real usage and tone: American vs British, formal vs casual

British style often uses ordinals with dates (5 May or 5th May). American formal prose prefers May 5. In business, spell out ordinals in running text and use numerals in tables, subject lines, and UI. Casual messages can use numerals freely.

Business letter: "Please deliver by 5 May" or "by May 5."
Signage/UI: "3rd Floor" or "3rd-floor entrance" for clarity.
Invitations/social: "Join us on July 4th."

Work: "Please submit the report by 5 May."
School: "Field trip on June 3rd - permission slips due Friday."
Casual: "Happy 30th birthday!"

Try your own sentence

Test the entire sentence rather than the isolated phrase. Context usually makes the correct form obvious.

Common errors and exact fixes (many wrong → right pairs)

Look for spaces before suffixes, wrong suffix choices, ordinals used instead of cardinals, and missing hyphens in compounds. Apply the right form consistently across the document.

Wrong: 11st →
Right: 11th
Wrong: 22th anniversary →
Right: 22nd anniversary
Wrong: 4 th place →
Right: 4th place
Wrong: She is 23rd years old. →
Right: She is 23 years old.
Wrong: I met him on the 25th of May. →
Right: I met him on 25 May. (formal) / May 25th (informal)
Wrong: 21 st century idea →
Right: 21st-century idea / the twenty-first century idea
Wrong: the number 4th in the list →
Right: the number 4 in the list / the fourth item in the list
Wrong: 1990's fashion →
Right: 1990s fashion

Fix your sentence: three-step checklist plus ready rewrites

Checklist: 1) Is it order or quantity? If quantity, use a cardinal. 2) Check the last two digits for 11-13. 3) Remove spaces, hyphenate compounds, or spell out for formality.

If it still sounds awkward, spell the ordinal out or move the phrase later in the sentence.

Checklist: Order vs quantity → 11-13 check → no space/hyphenation → style (spell out or numeral).
Prioritize clarity and consistency over mimicking casual forms.

Rewrite:
Original: "The 2nd quarter meeting is at 9." → "The second-quarter meeting is at 9:00 AM."
Rewrite:
Original: "I met him on the 25th of May." →
Formal: "I met him on 25 May." / Conversational: "I met him on May 25th."
Rewrite:
Original: "She finished 1st place in the contest." → "She finished in first place in the contest."
Work rewrite: "Send the 3rd draft by Friday." → "Send the third draft by Friday." or "Send draft 3 by Friday."
School rewrite: "Jacob is in his 2nd year at college." → "Jacob is in his second year of college."

Examples by context: ready-to-copy sentences for work, school, and casual use

Tone and format differ by channel. Below are three examples per channel with wrong → corrected forms.

Work:
Wrong: "Please join the 3rd Q meeting at 2." →
Right: "Please join the third-quarter meeting at 2:00 PM." or "Please join the 3rd-quarter meeting at 2:00 PM."
Work:
Wrong: "The 1st draft needs edits." →
Right: "The first draft needs edits." / "Draft 1 needs edits."
Work:
Wrong: "Locate the 2 nd file in the folder." →
Right: "Locate the 2nd file in the folder."
School:
Wrong: "Turn in by the 5th week." →
Right: "Turn in by week 5." or "Turn in by the fifth week."
School:
Wrong: "She's in her 3rd years." →
Right: "She's in her third year."
School:
Wrong: "Chapter 11th covers..." →
Right: "Chapter 11 covers..." or "The eleventh chapter covers..."
Casual:
Wrong: "Meet me on the 7 th." →
Right: "Meet me on the 7th."
Casual:
Wrong: "Happy 21st birthday!" →
Right: "Happy 21st birthday!" (no change)
Casual:
Wrong: "Our anniversary is the 11st." →
Right: "Our anniversary is the 11th."

Memory tricks and a pocket reference

Two quick aids: (1) Check the last two digits first-11, 12, 13 → -th. (2) Otherwise, use the last digit: 1→st, 2→nd, 3→rd, else→th.

No space: write 4th.
11, 12, 13 → th.
Hyphenate before nouns: 21st-century idea.
Spell small ordinals (first-tenth) in formal prose.

Cheatsheet: 1st, 2nd, 3rd, 4th-10th, 11th-13th, 14th-20th, 21st, 22nd, 23rd, 24th...
Trick: 21 → 21st (last digit). 111 → 111th (last two digits 11 → -th).

Similar mistakes to watch for (apostrophes, plurals, misplaced ordinals)

Apostrophes indicate possession, not decades: write 1990s, not 1990's. Watch for ordinals used where a cardinal fits (e.g., "3rd years") and misplaced ordinals that confuse meaning.

Wrong: 1990's fashion →
Right: 1990s fashion.
Wrong: the number 3rd →
Right: the number 3 / the third number.
Wrong: She's in her 3rd years →
Right: She's in her third year.

FAQ

Should I write "May 5th" or "May 5"?

Formal American prose prefers "May 5." British and conversational styles use "5 May" or "May 5th." Pick the style your audience expects and stay consistent.

Do I put a space before "th" or "st"?

No. Attach the suffix directly: 4th, not "4 th."

Why is it 11th and not 11st?

Numbers ending in 11, 12, or 13 always take -th. Check the last two digits to apply this exception.

Is "3rd floor" acceptable in a business email?

"3rd floor" is fine in short notes or signage. In formal business letters, prefer "third floor." Consistency matters.

When should I spell out ordinals instead of using numerals?

Spell out small ordinals (first-tenth) in formal running text and at sentence starts. Use numerals in tables, headings, UI, and space-limited contexts.

Want a quick sentence check?

When unsure, run the three-step checklist: order vs quantity, check 11-13, remove spaces and hyphenate compounds. Small edits like these make writing look polished.