Diameter Symbol (⌀): Meaning, ⌀ vs Ø, and How to Type It on Windows, Mac, Word, LaTeX

The diameter symbol (⌀) is a circle with a diagonal slash through it, placed before a dimension to say "this number is a diameter, not a width or a radius." You see it on engineering drawings (⌀25), on drill bits and bolts, on pipe specifications, and in CAD software, yet almost nobody can type it. The keyboard has no key for it, Windows has no Alt code for it, and most people use the Danish letter Ø instead, which looks nearly the same but is a different character.

This guide explains what the diameter sign means, which Unicode character is the right one, why Ø, ø, ∅, and φ keep getting mixed up with it, and how to type ⌀ on Windows, Mac, iPhone, Android, Word, Google Docs, Excel, HTML, and LaTeX, starting with a block you can copy and paste.

Diameter Symbol Copy and Paste

Copy the character you need from here:

1⌀
2⌀25
3S⌀40
4Ø
5ø
Copy

The first three lines use the DIAMETER SIGN, Unicode U+2300, the correct engineering symbol. The last two are the Latin letter O with stroke (U+00D8 and U+00F8), included because many fonts and legacy systems only accept those.

What the Diameter Symbol Means

Diameter is the distance across a circle through its centre, twice the radius. On a drawing, a bare number is ambiguous: 25 could be a length, a width, or a hole size. ⌀25 says unambiguously that the feature is circular and 25 units across.

Both major drawing standards use it the same way. ISO 129-1 (the dimensioning standard that works alongside ISO 128) and ASME Y14.5 in the United States place ⌀ directly before the value, with no space, as in ⌀25 or ⌀.500. Related conventions:

• R before a value is a radius: R12.5 is a 12.5 mm radius
• S⌀ is a spherical diameter: S⌀40 is a ball 40 mm across
• SR is a spherical radius
• ⌀ combines with tolerances, as in ⌀25 H7 or ⌀25 ±0.05

Pipe sizing is the one place the symbol is avoided on purpose. Pipes are specified by nominal size, DN in millimetres (DN50) or NPS in inches (2"), and those numbers are labels, not measured diameters: a DN50 steel pipe has an outside diameter of 60.3 mm. When a drawing needs the real dimension, it uses ⌀60.3.

In CAD the symbol is usually generated for you. AutoCAD adds ⌀ automatically to diameter dimensions, and in any text or dimension override you can type the control code %%c to insert it (%%d gives the degree sign, %%p gives ±). SolidWorks, Inventor, and Fusion 360 offer it in their symbol menus.

⌀ vs Ø vs ø vs ∅ vs φ

Six characters look like a slashed circle, and only one is the diameter sign. Search engines treat them as different text, fonts render them at different heights and widths, and screen readers announce them differently.

Why Ø is used so often. The letter Ø has been in every Western character set since the 1980s, so it displays in every font and survives every copy-paste. ⌀ lives in the Miscellaneous Technical block of Unicode and is missing from many fonts, where it shows as an empty box. That makes Ø a reasonable substitute in emails, spreadsheets, and part descriptions that pass through systems you do not control. On formal drawings and in anything that will be searched or parsed, use ⌀.

Why ∅ is wrong. The empty set sign is a mathematical symbol, usually drawn with a longer slash that extends beyond the circle. It sits next to ⌀ in symbol menus and gets picked by mistake.

Why φ keeps appearing. Typewriters and early CAD fonts had Greek letters but no diameter sign, so phi became a stand-in, and "phi 25" is still spoken aloud in many workshops. It is understood, but it is not what ISO or ASME specify. If you inherit a drawing with φ on it, it almost certainly means diameter.

How to Type the Diameter Symbol

Windows

There is no Alt code for ⌀, because Alt codes only cover the 256 characters of the Windows-1252 code page. The codes you will see recommended produce the Danish letter instead:

• Alt + 0216 gives Ø (capital O with stroke)
• Alt + 0248 gives ø (small o with stroke)

Both need Num Lock on and the numeric keypad, not the row of digits above the letters.

To get the real ⌀ on Windows:

1. Character Map: open the Start menu, type "Character Map," tick Advanced view, search for "diameter," select ⌀, and click Copy.
2. In Word or Outlook: type 2300 and immediately press Alt + X.
3. Copy it from the block at the top of this page.

Mac

• Option + Shift + O gives Ø
• Option + O gives ø

For the true diameter sign, open the Character Viewer with Control + Command + Space (or Edit > Emoji & Symbols), search for "diameter," and double-click ⌀.

iPhone and Android

On the iPhone keyboard, press and hold the O key. The popup shows accented variants including ø, and Ø with shift active. Gboard on Android works the same way: long-press O and slide to ø or Ø.

Neither mobile keyboard offers ⌀. Paste it from this page, or add a text replacement (Text Replacement on iOS, Personal dictionary in Gboard) that expands dia into ⌀.

HTML and Unicode

On Linux desktops and Chromebooks, press Ctrl + Shift + U, type 2300, and press Enter to insert ⌀ directly.

Word and Google Docs

Microsoft Word:

1. Type 2300 and press Alt + X to convert it into ⌀. This is the fastest method and works in Word on Windows and Mac.
2. Go to Insert > Symbol > More Symbols, pick a font such as Segoe UI Symbol or Cambria Math, choose the Miscellaneous Technical subset, and double-click ⌀.
3. For Ø, Alt + 0216 works as in any Windows program, or type 00D8 then Alt + X.

For frequent use, add an AutoCorrect entry that replaces (dia) with ⌀.

Google Docs: go to Insert > Special characters, type "diameter" in the search box, and click ⌀. Tools > Preferences > Substitutions can map a shortcut like ^dia to ⌀.

Excel and Google Sheets: =UNICHAR(8960) produces ⌀, =UNICHAR(216) produces Ø, and =UNICHAR(248) produces ø. To label hole sizes without changing the numbers, apply a custom number format such as "⌀"0.00; the cell shows ⌀25.00 but still contains 25.

LaTeX

LaTeX has no built-in diameter command. The honest summary is that wasysym provides the symbol actually called "diameter," while most people reach for lookalikes from packages they already have loaded.

1\usepackage{wasysym}   % provides \diameter (math mode)
2\usepackage{amssymb}   % provides \varnothing (math mode)
3
4Hole: $\diameter 25$ H7            % the correct diameter sign
5Shaft: $\varnothing 25$            % the empty set sign, visually similar
6Legacy: \O 25 and \o 25            % Danish letter O with stroke, text mode
Copy

A few notes on each option:

• \diameter (wasysym) draws the engineering diameter sign. It is a math-mode symbol, so wrap it in $...$. This is the right choice for part specifications and anything that claims ISO or ASME compliance.
• \varnothing (amssymb) and \emptyset are the empty set. Many engineering theses use them and most readers never notice, but they are semantically the wrong character, and \emptyset in Computer Modern looks more like a zero.
• \O and \o are text-mode commands for the Danish letters Ø and ø. They need no package and look fine in running text; in math mode use \text{\O} with amsmath.

To type ⌀ directly in a pdfLaTeX source, tell inputenc what to do with it:

1\usepackage{wasysym}
2\DeclareUnicodeCharacter{2300}{\ensuremath{\diameter}}
3
4Bore the hole to ⌀25 and chamfer the edge.
Copy

With XeLaTeX or LuaLaTeX and fontspec, ⌀ works directly if the font contains the glyph; DejaVu Sans does.

Frequently Asked Questions

What is the Alt code for the diameter symbol?

There is none for ⌀. Alt + 0216 gives Ø and Alt + 0248 gives ø, which are Latin letters that look similar. To get the true diameter sign on Windows, use Character Map or type 2300 followed by Alt + X in Word.

Is Ø the same as the diameter symbol?

No. Ø (U+00D8) is a letter of the Danish, Norwegian, and Faroese alphabets; ⌀ (U+2300) is the diameter sign. Ø is widely accepted as a substitute, but drawing standards specify ⌀.

What does ⌀25 mean on a drawing?

A circular feature, such as a hole or shaft, 25 units in diameter, usually millimetres. R25 would be a 25 mm radius and S⌀25 a 25 mm sphere.

What is the diameter symbol in LaTeX?

\diameter from the wasysym package, used in math mode. \varnothing (amssymb) and \emptyset are the empty set sign and only look similar. \O prints the Danish letter Ø in text mode.

What is the diameter symbol in HTML?

⌀ or ⌀ for ⌀. For Ø use Ø and for ø use ø.

Writing Technical Documents with Symbols

Diameters, radii, and tolerances fill engineering reports and theses, and getting the real ⌀ into every one by hand is tedious. Using the correct character keeps your documents searchable, standards-compliant, and consistent with the drawings they describe.

Octree is an AI-powered LaTeX editor that handles symbols and packages for you, so you can write "a 25 mm diameter hole" and get ⌀25 properly typeset in the output.

Create professional documents at https://app.useoctree.com