Inch and foot marks (″ ′)
The inch mark is a double prime (″) and the foot mark a single prime (′), so 5′ 10″ means five feet ten inches. The same marks stand for minutes and seconds of an angle, as in latitude and longitude. They are often typed as straight quotes (' and "); Butterick’s Practical Typography calls curly quotation marks (’ ”) in their place wrong.
Easily confused with
- Apostrophe (’)The apostrophe (’) is the raised comma-shaped mark in words such as it’s, Sam’s and ’90s. It shows that letters or numbers have been left out, and it forms possessives. On a keyboard it is usually typed as a straight mark ('), which is a different character from the curly apostrophe of printed text.
- Quotation marks (“ ”)Quotation marks (“ ” and ‘ ’), also called quotes, quote marks, speech marks or, in Britain, inverted commas, enclose words that someone said or wrote, and words used in an unusual sense. American style puts double marks first and commas and full stops (periods) inside them; British book style often puts single marks first, with full stops outside unless they belong to the quotation.
How to read it
Unicode names them U+2032 PRIME, “= minutes, feet”, and U+2033 DOUBLE PRIME, “= seconds, inches”, and cross-refers them to the straight apostrophe and quotation mark that stand in for them on keyboards. The American Heritage Dictionary defines a prime as a mark (′) placed above and to the right of a character, used for a unit such as feet or minutes of latitude and longitude, or to tell apart different values of the same variable in mathematics (x′). Butterick’s Practical Typography notes that the marks go by several names depending on what they label: foot and inch marks, minute and second marks, or prime and double prime. Unicode also has a triple prime ‴ (U+2034) for lines, an old measure of a twelfth of an inch. In metric terms an inch is 2.54 cm and a foot 0.3048 m (NIST). The US Government Publishing Office’s Style Manual and NIST write the units with the symbols in and ft.
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Prime, straight quote or curly quote?
| Mark | Unicode name | Code point | What it is for |
|---|---|---|---|
| ′ | Prime | U+2032 | Feet, and minutes of an angle |
| ″ | Double prime | U+2033 | Inches, and seconds of an angle |
| ' | Apostrophe | U+0027 | The straight keyboard mark, standing in for the prime and the apostrophe |
| " | Quotation mark | U+0022 | The straight keyboard mark, standing in for the double prime and quotation marks |
| ’ | Right single quotation mark | U+2019 | The curly Apostrophe (’) and closing single quote |
| ” | Right double quotation mark | U+201D | The closing curly quotation mark |
Butterick shows the difference with a longitude. Written with true primes, –118° 19′ 36.9″ is the purist’s version. With straight quotes, –118° 19' 36.9", it is “close enough”, and he calls straight quotes the most reliable choice because many professional fonts have no true primes. With curly quotes, –118° 19’ 36.9”, it is wrong. A true prime is a straight stroke with a slight northeast-to-southwest slope. Smart-quote software adds to the confusion, Butterick notes, by curling a typed foot or inch mark as if it were a quotation mark.
Minutes and seconds of an angle
A degree is divided into 60 minutes and a minute into 60 seconds, and the same marks label them (Butterick). NIST’s guide to SI units uses ' for the minute and " for the second of an angle, and the GPO Style Manual sets no space between a figure and the degree, minute and second signs, as in 33°15'21". The degree sign page shows the full form, 30°22′8″.
Look-alikes
Unicode cross-refers the double prime to the ditto mark 〃 (U+3003), and the prime to the acute accent ´ (U+00B4) and the modifier letter prime ʹ (U+02B9), which some older dictionaries used to mark a stressed syllable. Hebrew has its own geresh ׳ and gershayim ״, which Unicode prefers to the straight quotes when writing Hebrew.
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Sources
- General Punctuation: Range 2000–206F (code chart), The Unicode Standard, Version 18.0, Unicode Consortium, General Punctuation, 2032–2034
- C0 Controls and Basic Latin: Range 0000–007F (code chart), The Unicode Standard, Version 18.0, Unicode Consortium, Basic Latin, 0022 and 0027
- Chapter 6, Writing Systems and Punctuation, The Unicode Standard, Version 18.0.0, Core Specification, Unicode Consortium, §6.2.7 Apostrophes; §6.2.8 Hyphenation Point and Dictionary Syllabification
- prime (American Heritage Dictionary entry), The American Heritage Dictionary of the English Language, Fifth Edition, HarperCollins Publishers, prime, n. 4
- Foot and inch marks, Matthew Butterick, Butterick’s Practical Typography, Matthew Butterick, Foot and inch marks
- Type Talk: The Definitive Guide to Smart Quotes, Ilene Strizver, Type Talk, CreativePro, CreativePro, Q&A
- Guide for the Use of the International System of Units (SI), NIST Special Publication 811 (2008), National Institute of Standards and Technology, Appendix B.6 and B.8–B.9 (conversion factors); §7.2
- U.S. Government Publishing Office Style Manual (2016), GPO Style Manual, 2016 edition, U.S. Government Publishing Office, Rules 9.3 and 9.56
Last reviewed October 8, 2026 by Rory Hansen. How we research
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