What gauge extension cord should I use for a 15-amp table saw at 100 feet?

Use a 10-gauge cord. A 12-gauge cord might technically handle 15 amps, but at 100 feet the voltage drop will cause your saw to run sluggish, overheat the motor, and trip breakers more often. A 10-gauge cord keeps voltage loss under 3% at full load, giving you full power to the blade. Don’t even think about 14-gauge — that’s a fire and frustration starter.