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⌀

diameter sign

Diameter Sign

On a technical drawing, ⌀ before a number means the measurement runs across a circle through its center. It specifies a diameter rather than a radius. CAD can display a similar but separate character in its place, so exact character identity can matter.

Text symbol

Also called: diameter symbol · dia symbol
Search it as: diameter mark · AutoCAD diameter symbol · CAD diameter sign · diameter symbol drawing · diameter character · diameter symbol missing
Shows up in: Anything that takes text · its shape is whatever your font draws

What ⌀ means

⌀ marks the measurement as a diameter: ⌀20 means a circular feature measures 20 units across, not a radius of 20 units. Put the sign before its number on a drawing.

The same callout can specify the diameter of a counterbore (a flat-bottomed recess) or a countersink (a cone-shaped recess). The international standards trail includes an engineering-drawing recommendation from 1959, a 1985 revision, and ISO 129-1:2018, which sets general principles for presenting dimensions and tolerances.

⌀, Ø, and ∅ are distinct characters

Ø is a slashed Latin letter used in Scandinavian writing; ∅ denotes the empty set in mathematics. Unicode cross-references their related shapes, but they are separate characters. Use ⌀ when a drawing or application calls for the diameter sign.

This is precise engineering-drawing notation, not a conversational symbol.

For exact character identity, do not swap it casually for Ø or ∅.

Don't confuse it with

Latin Capital Letter O With Stroke

A slashed Latin letter used in Scandinavian writing; it is a letter, not the dedicated diameter character.

∅

Empty Set

This denotes the empty set in mathematics. AutoCAD 2025 documentation maps its diameter control code to this distinct character.

Questions people ask

Why can AutoCAD show ∅ for a diameter?

AutoCAD 2025 documentation maps its diameter control code to U+2205, the empty-set character. That code can therefore insert a character distinct from ⌀.

How to type ⌀

Windows (Word)

Alt+XType 2300, then Alt+X to get ⌀.

Windows

Win+Rrun charmap for the full table, or use the emoji picker's Ω symbols tab (Win + .).

macOS

Control+Command+SpaceOpen the character viewer and search “diameter sign”.

Linux

Ctrl+Shift+UType 2300, then Enter or Space.

HTML

⌀

CSS

\2300

AutoCAD legacy

In AutoCAD text or dimension content, enter %%C for the diameter control code.

AutoCAD Unicode

Use AutoCAD's Unicode-string entry or its Symbol menu.

Missing glyph

If ⌀ appears blank or as a box, try a font that includes it; verify U+2300 when exact character identity matters.

Codes and encoding1 code points

HTML decimal

⌀

HTML hex

⌀

CSS content

content: "\2300";

Each escape is closed by the next backslash; a trailing space is needed before a literal hex digit.

URL encoded

%E2%8C%80

On screen

Code points

JS .length

UTF-8 bytes

A visible symbol can contain several code points. JS .length counts UTF-16 units; UTF-8 counts bytes.

Families this belongs to

Maths & numbers1,835 symbols

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