You want to write 25° in a cell, then below are 2 ways to do it.
= 25 & CHAR(176)
= 25 & CHAR(176) & "F" (to insert Fahrenheit also)
= 25 & CHAR(176) & "C" (To insert Celsius also)
This approach will change the value to a character.
But if you want only to display degree symbol but want to keep underlying value to numeric, then copy the below and paste into custom format.
0°
0°F (to insert Fahrenheit also)
0°C (To insert Celsius also)
Sample File – Tips & Tricks 211