The degree symbol ° is used for temperature (25°C), angles (90°), and geographic coordinates. It is one of those characters everyone needs but few know how to type.
Windows Keyboard Shortcut
Hold Alt and type 0176 on the numpad (not the number row). Release Alt and ° appears. Make sure Num Lock is on.
Mac Keyboard Shortcut
Press Option + Shift + 8. Works in every app on Mac.
iPhone
Switch to the numbers screen (tap 123), then hold the 0 key. A popup appears with ° — slide to it and release.
Android
On most Android keyboards, switch to numbers/symbols and hold the 0 key. The degree symbol should appear as an option.
HTML and CSS
In HTML: ° or °. In CSS: \\00B0.
Should You Write °C or ℃?
Both are correct. °C (two characters) is more universally supported. ℃ (U+2103, a single precomposed character) is fine but slightly less compatible with older systems.