The diameter sign (⌀) that precedes circular dimensions on engineering drawings — plus the symbols people mistake for it. Click any symbol to copy it instantly.
The diameter symbol (⌀, Unicode U+2300) is the circle-with-a-slash mark that goes in front of a measurement to say "this is a diameter, not a radius." It shows up on machining specs, CAD drawings, and manufacturing callouts — and it's routinely swapped for lookalike characters that mean something else entirely.
The correct Unicode diameter sign, ready to paste in front of a measurement.
These look close enough to ⌀ to get substituted by accident — each one has a different meaning.
The diameter sign (⌀) is a graphical symbol standardized by ISO 7000 for engineering drawings, machining specs, and manufacturing callouts. Convention places it immediately before the numeric value — ⌀12 reads as "twelve millimeter diameter," not "radius twelve." That ordering is a hard rule in geometric dimensioning and tolerancing (GD&T); a radius uses the plain letter R instead, so swapping the two changes what a part actually measures.
Because ⌀ sits in the Miscellaneous Technical block rather than any legacy 8-bit character set, older CAD software and typewriter-era documentation often couldn't produce it directly. The workaround that stuck was substituting the visually similar empty set symbol ∅ (U+2205) instead — technically wrong, since ∅ means "no elements" in mathematics, but common enough that it still turns up on manufacturing drawings today.
| Platform / Tool | Method |
|---|---|
| AutoCAD | %%C — converts to ⌀ automatically |
| Word / Windows (Unicode input) | Type 2300, then press Alt+X |
| Windows (legacy NumPad Alt code) | Not available — ⌀ isn't in the Windows-1252 code page |
| Mac | Character Viewer (Cmd+Ctrl+Space), search "diameter" |
| HTML | ⌀ (no named entity exists) |
CSS content | content: "\2300" |
| LaTeX (wasysym package) | \diameter |
No. ⌀ (U+2300) is the diameter sign used on engineering drawings. Ø (U+00D8) is a Latin letter used in Danish, Norwegian, and Faroese, and appears in some physics notation for unrelated quantities. They just happen to look similar.
A lot of software and older documentation substitutes the empty set symbol ∅ (U+2205) for the true diameter sign because it's visually close and was easier to produce on older systems. It's technically incorrect — ∅ has its own mathematical meaning — but common enough in practice that you'll see it on real drawings.
Type %%C anywhere in a text or dimension string and AutoCAD converts it to ⌀ automatically. It's a legacy control code that predates Unicode input support and still works in current versions.
Before. ⌀12 is read as "twelve millimeter diameter." Placing it after the number isn't standard GD&T usage.
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