diameter symbol · dia symbol · diameter sign
⌀ Diameter Symbol
The diameter symbol ⌀ (Unicode U+2300, officially the DIAMETER SIGN) is the engineering mark that precedes a diameter measurement — ⌀25 means "25 units straight through the center". You will meet it on technical drawings, drill-bit packs and CAD dimensions. Click the card below to copy it.
Works on any device and browser — paste with Ctrl+V or Cmd+V.
How to type the diameter symbol ⌀ on any device
The diameter sign is on no standard keyboard, but every operating system has a way in. Pick your platform:
Windows
- Turn on Num Lock so the numeric keypad produces digits.
- Hold Alt, type 0216 on the numeric keypad, release Alt — Ø appears at the cursor, the standard stand-in for the diameter sign.
Tip: Windows has no universal alt code for ⌀ itself: Alt + 8960 works only in RichEdit-based apps like WordPad — most programs wrap or ignore codes above 255, so do not rely on it. In Word and other Office apps, type 2300 and press Alt + X for the real diameter sign; anywhere else, search "Character Map" in the Start menu (advanced view, search "diameter") — or simply copy ⌀ from the top of this page. The number row above the letters does not work for alt codes; it must be the keypad.
Mac
- Press Control + Command + Space to open the Character Viewer.
- Search "diameter" and double-click ⌀ to insert it at the cursor.
Tip: The Character Viewer works in every app. If you enable the Unicode Hex Input layout (System Settings → Keyboard → Input Sources), holding Option and typing 2300 also produces ⌀. Note that Option + O types ø (Shift + Option + O gives Ø) — the Scandinavian letter, a handy stand-in but not the diameter sign.
iPhone & iPad
- The stock iOS keyboard has no ⌀ key — tap the copy card at the top of this page instead.
- Paste the symbol wherever you need it with a long-press → Paste.
Tip: Type it often? Go to Settings → General → Keyboard → Text Replacement and map a shortcut like "dia" to ⌀ — it then works in every app.
Android
- Gboard and most stock keyboards do not include ⌀ — copy it from the card at the top of this page.
- Long-press a text field and tap Paste to insert it.
Tip: For repeated use, add ⌀ to Gboard’s personal dictionary (Settings → Dictionary) with a shortcut like "dia", or install a Unicode keyboard app.
Chromebook
- Press Ctrl + Shift + U to start Unicode input — an underlined "u" appears.
- Type 2300, then press Enter or Space to confirm.
Tip: ChromeOS also has an emoji and symbol picker (Search + ., i.e. Launcher + period), but its symbol coverage varies — if ⌀ is not listed, the Unicode input above always works, or copy it from this page.
Linux
- Press Ctrl + Shift + U in most GTK apps.
- Type 2300, then press Enter to insert the ⌀.
Tip: With a compose key configured, Compose + O + / produces Ø on most desktop environments; for ⌀ itself, use the Unicode input above.
In Word, Excel, AutoCAD & other apps
Office and CAD software add their own shortcuts on top of the system ones above.
Microsoft Word
- Type 2300 where you want the symbol.
- Press Alt + X — the code converts to ⌀ in place.
- Or go to Insert → Symbol → More Symbols → Miscellaneous Technical.
- Type it often? Set up AutoCorrect: File → Options → Proofing → AutoCorrect Options → replace "(dia)" with ⌀.
Tip: Alt + X also works in Outlook and PowerPoint, but not in Excel. On a Mac, use the Character Viewer (Control + Command + Space) in any Office app.
Microsoft Excel
- Click the cell (or press F2 to edit it).
- Hold Alt, type 0216 on the numeric keypad, release Alt — Ø appears in the cell as the diameter stand-in.
- Formula option for the true sign: =UNICHAR(8960) returns ⌀.
Tip: Excel does not support Word’s Alt + X shortcut. For drawings-style labels you can also insert ⌀ via Insert → Symbol.
AutoCAD
- In any text or dimension field, type %%c.
- AutoCAD renders it as the diameter symbol ⌀ automatically.
- In MTEXT you can also right-click → Symbol → Diameter.
Tip: The other classic %% codes: %%d gives the degree sign ° and %%p gives plus-minus ±.
Google Docs
- Go to Insert → Special characters.
- Search "diameter" (or draw the shape) and click ⌀.
Tip: Faster for repeated use: copy ⌀ once from this page and paste with Ctrl+V — or set up Tools → Preferences → Substitutions to auto-replace "(dia)" with ⌀. In Google Sheets, the formula =UNICHAR(8960) produces ⌀.
Rather not memorize shortcuts?
Bookmark this page and copy the symbol whenever you need it — it is faster than any alt code.
Diameter symbol ⌀ codes for developers
Every encoding of the diameter sign in one place — Unicode, HTML entities, CSS, JavaScript and URL encoding. Click any chip to copy it.
Unicode
| Format | ⌀ diameter sign |
|---|---|
| Code point | |
| Official name | |
| Block | |
| UTF-8 bytes | |
| UTF-16 |
HTML & XML
| Format | ⌀ diameter sign |
|---|---|
| Decimal entity | |
| Hex entity | |
| Named entity | none — use the decimal entity |
Programming
| Format | ⌀ diameter sign |
|---|---|
| CSS content | |
| JavaScript / JSON | |
| Python | |
| LaTeX (wasysym) | |
| URL percent-encoding |
Keyboard entry
| Format | ⌀ diameter sign |
|---|---|
| Word / Office (Windows) | |
| AutoCAD | |
| Ø substitute (Windows) |
- ⌀ lives in the Miscellaneous Technical Unicode block (U+2300–U+23FF), alongside ⌘ and ⏏. Unlike the currency signs, it is not part of Latin-1 — any modern UTF-8 system renders it, but very old 8-bit software cannot.
- There is no named HTML entity for ⌀ (no
⋄) — use⌀or⌀. Beware of∅: it renders ∅, the empty-set sign, which is a different character. - Ø and ø (U+00D8 / U+00F8) are letters from the Danish and Norwegian alphabets. They are the classic stand-ins when ⌀ is unavailable, and the only lookalikes with a true Windows alt code — but typographically they are letters, not the diameter sign.
The diameter sign: a drafting-room classic
A circle with a slash
The ⌀ — also called the dia symbol or the "circle with stroke" — marks the diameter of a circular feature on engineering drawings — a circle (the end view of a cylinder) crossed by a stroke. Dimensioning standards such as ISO 129 and ASME Y14.5 place the sign directly before the value, with no space: a hole labelled ⌀8 is 8 units across. The convention saves the word "diameter" thousands of times on a single drawing, which is why the dia symbol became one of the most-recognized marks in manufacturing. A sphere is dimensioned with S⌀ ("spherical diameter"); a radius gets no symbol at all, just a capital R.
⌀ vs Ø vs ∅: three lookalikes
Unicode holds three characters that all look like a slashed circle. The diameter sign ⌀ (U+2300) is the technical symbol. Ø and ø (U+00D8 / U+00F8) are letters of the Danish and Norwegian alphabets — borrowed for decades as the diameter stand-in because they sit on the old code pages and have real alt codes. And ∅ (U+2205) is the empty-set symbol from mathematics, usually drawn taller with a steeper slash. On a drawing or spec sheet, reach for ⌀; when the font or system cannot show it, Ø is the accepted substitute — but ∅ never is. A fourth lookalike, ⊘ (U+2298 CIRCLED DIVISION SLASH), keeps its slash inside the circle and belongs to math notation, not drawings. And the Greek letter φ (phi) is a false friend of its own: "phi symbol" is a common misnomer for ⌀, since some fonts draw phi as a stroked circle — but phi's stroke is vertical, while the diameter sign's slash runs at 45°.
| Symbol | Name | Unicode | Key difference |
|---|---|---|---|
| ⌀ | Diameter sign | U+2300 | The correct one — slash crosses the circle at 45° |
| Ø | Scandinavian letter O with stroke | U+00D8 / U+00F8 | Accepted stand-in — but a letter, not the sign |
| ∅ | Empty set | U+2205 | Math only — taller glyph, steeper slash |
| ⊘ | Circled division slash | U+2298 | Math notation — slash stays inside the circle |
| φ | Greek letter phi | U+03C6 | "Phi symbol" misnomer — phi's stroke is vertical |
The dia symbol in the wild
You will meet the ⌀ on drill-bit packaging and tap sets, on pipe and fittings specs, in CNC and 3D-printing files, and across every kind of CAD drawing — AutoCAD users know it best as the %%c code. It appears wherever a circle's size matters: ⌀25 bearings, ⌀ 10 mm dowel holes, 2× ⌀8 mounting patterns. Click any example below to copy it:
The symbol always precedes the value — ⌀25, never 25⌀ — and in dimension lines it sits tight against the number, often in the drawing's own technical lettering.
Correct usage
- ✓
⌀50mm - ✓
⌀ 100cm - ✓
Pipe ⌀75 - ✓
Hole ⌀6.35 - ✓
⌀25.4±0.1mm(with tolerance)
Avoid
- ✗
50mm⌀(symbol after the value) - ✗
DIA 50mm/D=50mm(text stand-ins) - ✗
∅50mm(empty-set sign — wrong character)
Ø50mm is not the standard form, but is a tolerated substitute when ⌀ cannot be typed or displayed.
Frequently asked questions
How do I copy the ⌀ diameter symbol?
Click the ⌀ card at the top of this page and the diameter symbol is copied to your clipboard instantly. Then paste it anywhere with Ctrl+V (Windows) or Cmd+V (Mac).
What is the alt code for the diameter symbol?
There is no universal Windows alt code for ⌀ itself — it sits outside the legacy code pages. Alt + 8960 works in RichEdit-based apps such as WordPad, but most programs wrap or ignore codes above 255, so do not rely on it. The classic stand-in is Ø: hold Alt and type 0216 on the numeric keypad (Alt + 0248 gives lowercase ø). In Word and other Office apps, type 2300 and press Alt + X to get the real diameter sign.
What is the difference between ⌀, Ø and ∅?
Three lookalikes, three different characters. ⌀ (U+2300 DIAMETER SIGN) is the engineering symbol for the diameter of a circular feature. Ø/ø (U+00D8/U+00F8) is a letter of the Danish and Norwegian alphabets, widely used as a diameter stand-in. ∅ (U+2205 EMPTY SET) is a math symbol — usually drawn taller with a steeper slash. For drawings and specs, ⌀ is the correct one; Ø is the accepted substitute; avoid ∅.
Is the diameter symbol the same as φ (phi)?
No. φ (U+03C6) is a letter of the Greek alphabet, used for angles, the golden ratio and physics quantities. "Phi symbol" is a common misnomer for ⌀ because some fonts draw phi as a stroked circle — but the diameter sign is U+2300, and its slash runs diagonally at 45°, not vertically.
How do I write a diameter with tolerances?
The symbol comes first, then the value, then the tolerance and unit: ⌀50±0.1 mm, or ⌀50 +0.1/−0.05 mm for bilateral tolerances. Never put the symbol after the number (50 mm ⌀), and on drawings avoid text stand-ins like "DIA" or "D=" — ⌀ is the standardized form.
How do I type the diameter symbol in AutoCAD?
Type %%c in any text or dimension field and AutoCAD renders it as ⌀. The other two %% codes are %%d for the degree sign ° and %%p for plus-minus ±. In MTEXT you can also right-click → Symbol → Diameter.
How do I type ⌀ in Word, Excel or Google Docs?
In Microsoft Word, type 2300 and press Alt + X — the code turns into ⌀. In Excel, use the formula =UNICHAR(8960) or the Ø alt code Alt + 0216 inside a cell. In Google Docs, go to Insert → Special characters and search "diameter".
What is the Unicode for the diameter symbol?
The diameter sign is U+2300 (DIAMETER SIGN) in the Miscellaneous Technical block. In HTML write it as ⌀ or ⌀ — there is no named entity. In UTF-8 it is the three bytes E2 8C 80; percent-encoded in a URL it is %E2%8C%80.
How do I type ⌀ on a Mac?
Press Control + Command + Space to open the Character Viewer, search "diameter" and double-click ⌀. If you enable the Unicode Hex Input keyboard layout (System Settings → Keyboard → Input Sources), you can also hold Option and type 2300.
How do I type the diameter symbol on an iPhone or Android phone?
Neither iOS nor Gboard puts ⌀ on the stock keyboard, so the fastest way is to copy it from this page. For regular use, set up a text replacement: on iPhone go to Settings → General → Keyboard → Text Replacement and map "dia" to ⌀; on Android add the same shortcut in Gboard’s personal dictionary.
What does ⌀ mean on a drawing or a spec?
It marks a diameter: the width of a cylindrical or circular feature measured straight through the center. The sign always precedes the value — ⌀25 means "25 mm (or units) in diameter". A sphere gets S⌀ ("spherical diameter"), while a radius is written with a plain R, as in R10.
Why does ⌀ show up as an empty box?
The box (called "tofu") means the current font does not contain U+2300. It is not in classic body fonts like Times New Roman or Arial; fonts that do carry it include Segoe UI Symbol (Windows), Apple Symbols (macOS), Noto Sans Symbols and DejaVu Sans. If your audience may be on old systems, fall back to Ø.
Is there a radius symbol to go with ⌀?
No — Unicode has a diameter sign but no dedicated radius sign. Engineering drawings simply use a capital R in front of the value (R5 means a 5 mm radius), while ⌀ is reserved for diameters and S⌀ for spherical diameters.
How do I write the diameter symbol in LaTeX?
Load the wasysym package and use \diameter. Be careful not to reach for \varnothing — that renders ∅, the empty-set symbol, which is a different character with a steeper slash.
Download the diameter symbol
Free ⌀ artwork in three formats — for designs, documents and print. No attribution required.
