Windows: hold Alt and type 0176 on the numeric keypad
Mac: press Option + Shift + 8
iPhone/iPad: press and hold 0, then select °
Android: press and hold 0 or use the symbols keyboard to find °
Linux: press Ctrl + Shift + U, type 00b0, then press Enter
Microsoft Word: type 00B0 and press Alt + X
Copy and paste this symbol: °