What gauge extension cord should I use for a 15-amp circuit over 50 feet?

Use a 12-gauge cord for runs longer than 50 feet on a 15-amp circuit. A 14-gauge cord at 50 feet loses about 3% voltage at full load, which can weaken tools and overheat motors. A 12-gauge cord keeps voltage drop under 3% at 100 feet. Never daisy-chain cords to extend length.