50 feet is the max for a 16-gauge cord at 10 amps—but 25 is safer.

Stick to 25 feet if you can; 50 feet is the absolute limit before voltage drop becomes noticeable.

Voltage drop is real. At 50 feet, a 16 AWG extension cord running 10 amps will lose about 4 volts on a 120V circuit. That’s around 3.3% drop—technically within the 5% “acceptable” range, but your tool will run slightly slower and the cord will get warmer. At 100 feet you’re looking at 8 volts dropped, which is too much for most power tools and could damage them over time.

The math is straightforward: 16-gauge copper wire has about 4 ohms per 1000 feet. Voltage drop = (2 × length × current × resistance) / 1000. At 50 feet that’s 4V. At 25 feet it’s only 2V. Your tool barely notices 2V.

If you need to go farther, step up