About empty set
The empty-set sign denotes a set with no elements. It is not the slashed letter Ø or the diameter sign ⌀, despite their similar appearance.
How to type ∅
Source-checked methodsMicrosoft Word
Windows desktopUnicode conversion in Word for Windows
Type 2205, select those hexadecimal digits, then press Alt + X to insert ∅.
Applies to Word for Windows. Use a font that contains the character. This is Unicode conversion, not a Windows Alt code.
Source documentationmacOS
Character ViewerCharacter Viewer
Choose Edit → Emoji & Symbols, search for “empty set” or its code 2205, then select the character to insert it.
Expand Character Viewer if needed. Available characters depend on font support.
Apple documentationMicrosoft Excel
Formula=UNICHAR(8709)
Enter =UNICHAR(8709) in a cell to return ∅.
Excel 2013 or later. The English function name is shown; localized Excel may use another name. Paste values if you need text without a formula.
Source documentationGoogle Docs
Desktop pickerInsert → Special characters
On a computer, choose Insert → Special characters and search for U+2205 or empty set. Select the matching symbol.
Google Docs and Slides on desktop. If the picker does not offer the symbol, copy it here and paste it into your document.
Source documentationLinux
GNOME / GTKCtrl + Shift + U, 2205, Enter
In a compatible GNOME/GTK text field, press Ctrl + Shift + U, release the keys, type 2205, then press Enter.
Applies to GNOME/GTK Unicode entry, not every Linux application. Use copy and paste when the app intercepts this shortcut.
Source documentationFor iPhone and Android, you can copy the character above and paste it into an app that supports it.
Using it in HTML
Insert ∅ in HTML text, or paste ∅ directly in a UTF-8 document. If a box appears instead of the character, choose a font with support for U+2205.