What gauge of wire do I need to run off a 20 amp breaker?

#12

#12

Is there a way to find out gauge of wire to amps, or is it something I should just learn to know it? I was just curious on how you find this out or if it's something you just remember. I have little experience in this area.

I use Table 310.16 of the National Electric Code. A link can be found in the Sticky Note "Read This First" of the Electrical Forum, along with instructions on exactly how to get to it.

Breakers need to be weaker than the wire.
You can use larger wire to reduce voltage drop.
#10 30 Amps
#12 20 Amps
#14 15 Amps
The Info provided by TK shows the rest.