⌀ Diameter Symbol
The diameter sign (⌀) marks a diameter on an engineering drawing. It is not the letter Ø, not the empty set ∅, and not a Greek phi — those are the four characters everyone mixes up.
Also known as: diameter sign, diameter symbol, dia symbol, phi diameter.
Codes
| Symbol | ⌀ | |
| Unicode | U+2300 | |
| HTML entity (decimal) | ⌀ | |
| HTML entity (hex) | ⌀ | |
| CSS | \2300 | |
| LaTeX | \diameter | |
| Windows Alt code | Alt + 8960 |
How to type ⌀ (Diameter Symbol)
In Word, type 2300 then press Alt + X. Elsewhere, copy ⌀ above or use Character Map (search “diameter”).
⚠️ Do not use Option + Shift + O — that gives Ø (U+00D8), the Danish letter, which is the single most common wrong answer here. There is no keystroke for ⌀: copy it above, or use Character Viewer (Control + Cmd + Space) and search “diameter”.
Type 2300, then press Alt + X to convert it to ⌀.
Insert → Special characters, then search “diameter”.
There is no diameter sign in core LaTeX. \diameter comes from the wasysym package. (\varnothing is the empty set ∅ — a different symbol.)
Usage
- On a technical drawing, ⌀25 means a hole or shaft 25 mm across. It always precedes the value, and ISO 129 calls for it wherever a dimension is a diameter rather than a radius.
- Which one to use — four characters look alike and only one is the diameter sign: ⌀ (U+2300) is the diameter sign. Ø (U+00D8) is the Danish/Norwegian capital letter O with stroke. ∅ (U+2205) is the empty set in mathematics. φ (U+03C6) is Greek phi. They are not interchangeable, though drawings in the wild use all four.
- The letter Ø is the usual substitute, because it is on the keyboard (Option + Shift + O on a Mac) and ⌀ is not. It renders acceptably and most machinists will read it, but it is the wrong character: it will not match a search for the diameter sign, and it carries a language, not a meaning.
- The circle-with-slash of ⌀ leans the same way as the one in Ø, which is why the eye cannot separate them. Check the code point, not the glyph.