What gauge for a 100-foot extension cord

A hundred feet of copper is a resistor you can hold. On 120 V, a 15 A load through 14 AWG drops about 9.2 V (7.7%) — enough that a saw or compressor feels like it lost a size. The same load on 10 AWG is about 3.6 V (3.0%). That is why long-run shopping starts at gauge, not at “outdoor yellow, 100 ft.”

Planning drops at 100 feet, 120 V

These use the same NEC Chapter 9 Table 8 copper numbers as the master chart. They are not a lab report for a named reel.

When 12 AWG is enough at 100 feet

• Loads around 10 A: lights, a radio, a charger, a small drill that is not bound up.
• You accept ~3.9 V (3.2%) at 10 A, which is still in a comfortable band.
• The cord is marked for the amps, fully unspooled, and the connections are tight.

A 15 A circular saw at 100 feet is not that job. Use 10 AWG, or move power closer. See the saw guide.

When 10 AWG is the honest pick

• 13–15 A motor tools at a full 100 feet.
• Anything that already dimmed lights on a shorter 12 AWG run.
• A compressor or similar load that starts hard. Nameplate understates the first instant.

10 AWG 100-foot cords are heavy. That is the trade. If you cannot carry it, run a properly installed receptacle closer to the work instead of stacking light cords.

Outdoor 100-foot reels

Buy a weather-rated jacket if the cord lives outside — SJTW notes. The jacket does not reduce voltage drop. A 100-foot 16 AWG “outdoor” reel is still a 16 AWG resistor.

If the 100-foot choice is really 12 vs 14, the 12 vs 14 page is the short version: 14 AWG at 100 feet on 15 A is the wrong aisle.

50 ft 12 AWG SJTW is the usual shop buy for a 50-foot 15 A job. At a full 100 feet and 15 A the chart pick is 10 AWG, and we do not link a checked 10 AWG cord.