Prime ′ vs Apostrophe ‘ vs Right Single Quote ’: How to Tell Them Apart

The prime ′, straight apostrophe ‘, and right single quotation mark ’ can be difficult to distinguish at normal text sizes.

They may all appear as small raised strokes, but they are different Unicode characters and usually serve different purposes.

This is a case where visual appearance can suggest an answer, but the surrounding context and actual code point provide much stronger evidence.

Prime, Apostrophe, and Right Single Quote at a Glance

These characters belong to a wider group of punctuation and punctuation-like symbols in which several marks can look almost identical while carrying different meanings.

What Is the Prime Symbol ′?

′ is U+2032 PRIME.

It is primarily a technical symbol rather than ordinary quotation punctuation.

Unicode associates it with uses such as minutes and feet, and the prime is also widely used in mathematics and scientific notation.

Prime in Mathematics

A prime can distinguish a mathematical object from another related object or value.

For example:

x′

is commonly read as “x prime.”

In calculus:

f′(x)

commonly denotes the first derivative of a function.

A second derivative may be written with a double prime:

f″(x)

Prime notation has many other mathematical uses, so its precise interpretation still depends on context.

Prime in Angle Measurements

Prime and double prime are used in angular measurement:

° — degrees

′ — arcminutes

″ — arcseconds

For example:

30° 15′ 20″

Here the prime and double prime are measurement symbols, not quotation marks.

Prime for Feet and Double Prime for Inches

Prime and double prime are also used in notation for feet and inches.

For example:

6′ 2″

can represent six feet two inches.

The same characters therefore take on different technical meanings depending on whether the surrounding text describes an angle, a physical measurement, or a mathematical expression.

What Is the Straight Apostrophe ‘?

‘ is U+0027 APOSTROPHE.

It is available directly on most keyboards and has historically been used for several related purposes.

It can function as an apostrophe:

don’t

Alex’s

or as a single quotation mark in plain text:

‘quoted text’

Because it is easy to type, U+0027 is also commonly used as a plain-text substitute for prime notation.

Why Is ‘ Often Used Instead of ′?

The main reason is practical: the apostrophe ‘ is present on ordinary keyboards, while the prime ′ usually requires another input method.

As a result, you may see:

6′

where formally typeset measurement text might use:

6′

The first form is a common keyboard approximation. The second uses the dedicated Unicode prime character.

A reader may understand both immediately, but they are not the same encoded text.

What Is the Right Single Quotation Mark ’?

’ is U+2019 RIGHT SINGLE QUOTATION MARK.

In common English typography, it can close a single quotation:

‘quoted text’

Unicode also prefers U+2019 when an apostrophe is functioning as punctuation in typeset text:

don’t

Sarah’s

U+2019 therefore has more than one common punctuation role even though its character identity remains the same.

Prime ′ vs Right Single Quote ’

These two characters can be especially hard to distinguish because both may appear as a short raised stroke.

Compare:

′ — PRIME

’ — RIGHT SINGLE QUOTATION MARK

The prime is primarily used in technical notation. U+2019 is primarily punctuation.

Many fonts draw the prime as a more direct angled stroke and U+2019 as a more comma-like form, but that visual difference is not consistent enough to serve as a universal rule.

Prime ′ vs Straight Apostrophe ‘

These are also different characters:

′ — U+2032 PRIME

‘ — U+0027 APOSTROPHE

The straight apostrophe is often used as a convenient substitute for prime in informal or plain-text contexts.

That substitution may communicate the intended meaning to a reader without changing the fact that the encoded characters are different.

Straight Apostrophe ‘ vs Right Single Quote ’

U+0027 ‘ is the straight ASCII apostrophe.

U+2019 ’ is the typographic right single quotation mark and the Unicode-preferred character for a punctuation apostrophe in typeset text.

Compare:

don’t

don’t

The words have the same ordinary meaning, but they contain different apostrophe characters.

What About the Modifier Letter Apostrophe ʼ?

Another very similar character is:

ʼ — U+02BC MODIFIER LETTER APOSTROPHE

This character is used when an apostrophe-shaped mark functions as a modifier letter rather than ordinary punctuation. It appears in a number of orthographies and transliteration systems, including uses related to glottal stops and glottalization.

Some fonts make U+02BC and U+2019 almost indistinguishable. Their code points and linguistic functions are therefore more reliable identifiers than their shapes.

What Is the Double Prime ″?

″ is U+2033 DOUBLE PRIME.

It is commonly used for seconds of angle, inches, mathematical notation, and other technical purposes.

It should not be confused with:

“ — U+0022 QUOTATION MARK

or:

” — U+201D RIGHT DOUBLE QUOTATION MARK

All three can look like a pair of small raised strokes, but they are separate Unicode characters.

Double Prime ″ vs Two Prime Characters ′′

U+2033 DOUBLE PRIME is one Unicode character.

A sequence of two U+2032 PRIME characters is:

′′

Unicode records a compatibility relationship between the dedicated double-prime character and a sequence of two prime characters.

They are therefore closely related in meaning, but they are still different raw character sequences.

Why Fonts Make These Characters Hard to Distinguish

Unicode defines character identity, while fonts determine how those characters are drawn.

A font may render the prime as a sharply angled line, while another makes it more curved. A right single quotation mark can be strongly comma-shaped in one typeface and relatively straight in another.

At small text sizes, the differences may become almost invisible.

This is why rules such as “the prime is always straight” or “the apostrophe is always curved” are unreliable.

Why the Difference Matters in Measurements

Dedicated prime characters make the intended measurement notation explicit.

Compare:

5′ 10″

with the common keyboard approximation:

5′ 10″

A human reader can usually interpret either form, but the first uses PRIME and DOUBLE PRIME while the second uses APOSTROPHE and QUOTATION MARK.

Why the Difference Matters in Mathematics

Prime marks can carry mathematical meaning.

For example:

f′

uses U+2032 PRIME.

A plain-text form such as:

f’

uses U+0027 APOSTROPHE instead.

Both may be understood in informal mathematical text, but systems that care about exact character semantics can distinguish them.

Why the Difference Matters in Search and Data

Software does not necessarily treat prime, apostrophe, right single quotation mark, and modifier letter apostrophe as equivalent.

The distinction can affect:

• search and replace;
• string comparison;
• mathematical conversion;
• measurement data;
• database matching;
• text normalization;
• copy-and-paste workflows.

Two strings can appear nearly identical while containing different code points.

How to Tell Which Character You Have

Context is the first useful clue.

A mark after a number in a height measurement may be intended as a prime. A mark inside don’t is functioning as an apostrophe. A mark at the end of ‘quoted text’ is functioning as a closing single quotation mark.

But context tells you the intended role, not necessarily which character was actually typed. Keyboard substitutions are common.

For exact identification, check the code point:

If a copied mark is too similar to identify by eye, paste it into What Is This Symbol and inspect the actual character.

The Main Difference

The four most easily confused characters have different primary roles:

• ′ is a prime used in mathematical, measurement, and technical notation;
• ‘ is the straight ASCII apostrophe and a common plain-text single quotation mark;
• ’ is the right single quotation mark and the preferred punctuation apostrophe in typeset text;
• ʼ is a modifier letter rather than ordinary punctuation.

Context helps explain what a mark is meant to do. The Unicode code point tells you which character is actually present.