---
name: Prime mark
slug: prime-mark
category: typography
status: published
created: 2026-08-21T00:00:00.000Z
modified: 2026-08-21T00:00:00.000Z
definition: The slanted tick used for feet, inches, minutes, and seconds, which
  is a different character from either a straight quote or a curly one.
aliases:
  - name: primes
  - name: foot mark
  - name: inch mark
  - name: double prime
tags:
  - content-design
  - editorial
relations:
  contrastWith:
    - smart-quotes
    - superscript
  variantOf: []
  partOf: []
  seeAlso: []
implementations: []
sources:
  - title: Foot and inch marks (Practical Typography)
    url: https://practicaltypography.com/
  - title: Typography Cheatsheet (Typewolf)
    url: https://www.typewolf.com/cheatsheet
demo: inline
exhibit: false
useWhen: writing feet and inches, not quoting anyone
---

A prime is a short mark that leans to the right, and it means a unit: feet,
minutes of arc, minutes of time. Doubled, it means the next unit down: inches,
seconds. So a person is 5′ 10″ tall and a coordinate is 40° 44′ 55″ N. It is not
a punctuation mark and it is not an abbreviation. It is a symbol with its own
code points, U+2032 for the prime and U+2033 for the double prime, plus a triple
for the rare third level.

Three different marks get used for this job and only one of them is right. The
straight tick on the keyboard, U+0027, is the typewriter's apostrophe: upright,
symmetrical, and standing in for four marks at once because the machine had no
room for more keys. The curly ones, U+2019 and U+201D, are closing quotation
marks with comma-shaped tails, and they are what an editor with
[smart quotes](/smart-quotes) turns your straight ticks into. The prime is the
third thing: a straight stroke like the typewriter mark, but leaning, and with
none of the comma-shaped tail a closing quote curls into. Set the three side by
side at any size above a caption and they stop being confusable.

The confusion is the typewriter's fault and the substitution habit is the
autocorrect's. Nearly every writing tool now converts a straight tick to a curly
quote as you type, which is right for prose and exactly wrong for measurements,
so `5' 10"` becomes `5’ 10”` without asking. The result is a height written with
two closing quotation marks, which reads to a typographer roughly the way a
lowercase l used as a numeral one does. If a text field in your product accepts
measurements, this is worth a rule of its own: leave a tick alone when a digit
sits immediately before it.

For interface work, the practical advice is to store and render the real
characters rather than hope the font makes a substitute look acceptable. Most
text faces draw a proper prime; those that do not fall back to something visibly
different, which is at least an honest signal. And do not reach for a slanted
apostrophe from an italic font, which is the traditional hot metal workaround
and has no meaning in a Unicode world.