I am running a 120v line from my garage breaker box to my barn. The distance is 200 feet. I need the line for 3 lights and one plug. Can someone tell me what size wire I need to run that distance? I know there is an amp drop but I'm not sure how much it is per 100 feet.

#6 copper or #4 aluminum would be good for 15 amp circuit and just barely out of spec for a 20 amp circuit.