Twelve gauge is about the thickness of a nickel, and 14-gauge is about the thickness of a dime. Also, look at the breaker for the circuit in question to see if it's a 15-amp or a 20-amp breaker. A 20-amp circuit requires wire that's 12-gauge or larger.

Should I use 12 or 14 gauge wire?

As long as you don't put too many lights on the light circuit, you can usually control that circuit with a 15-amp breaker, as well as wire it with a 14-gauge wire. ... On the other hand, an outlet circuit controlled by a 20-amp breaker requires a 12-gauge wire.

What is 12 gauge wire used for?

12-gauge are used in kitchen, bathroom, outdoor receptacles, and 120-volt air conditioners supporting 20 amps. 10-gauge are used in electric clothes dryers, 240-volt window air conditioners, electric water heaters supporting 30 amps. 6-gauge are used for cook tops and ranges carrying 40-50 amps.