It depends on the model. The C172 P,R,S models have the following direction in
the "Normal Procedures" section in the "Wing Flap Settings".
Crikey, I don't fly stuff that modern. I should have clarified and said 'for the K and M models.'..and they still fly in MPH! The K I fly incidentally has 40 degrees of flap. Mmmm, nice.
Quite right though, the POH is your friend.
I always understood that flap settings above 10-15 degrees created more drag than lift.
Why use 25 degrees (Cessna don't).
The 182P in my logbook (I'll be model specific this time!) has flaps 20 for short field take off.