What Wire Gauge for a 20 Amp Circuit?
Almost every guide gives you the same one-line answer: 12 gauge. That's correct — but it's only half the story. On a long circuit run, 12 AWG isn't enough, and knowing when to jump up to 10 AWG is what separates a code-passing job from a nuisance-tripping, dimming-lights headache. Here's both parts.
A 20 amp circuit requires 12 gauge (12 AWG) copper wire as the minimum. Never use 14 AWG on a 20 amp breaker — it's only rated for 15 amps and is a fire hazard. On runs longer than about 100 feet, upsize to 10 AWG to control voltage drop.
Why 12 Gauge Is the Answer
Wire gauge measures thickness, and in the American Wire Gauge (AWG) system, a lower number means a thicker wire. Thicker wire carries more current without overheating. Every wire has an ampacity — the maximum current it can safely handle continuously.
12 AWG copper is rated for 20 amps, which matches a 20 amp breaker exactly. That's why the U.S. National Electrical Code (NEC) sets 12 AWG copper as the minimum branch circuit wire for 20 amp circuits in homes. The pairing is deliberate: the wire and the breaker are sized to protect each other.
The Part Most Guides Skip: Distance and Voltage Drop
Here's what a one-line "use 12 gauge" answer misses. Wire has resistance, and over a long run that resistance causes voltage to drop before it reaches the outlet. Too much voltage drop means dim lights, motors that run hot, and appliances that underperform or fail early.
The NEC recommends keeping voltage drop under 3% for branch circuits. On short runs, 12 AWG stays well within that. But as the run gets longer, voltage drop climbs — and at some point you have to move up to a thicker 10 AWG wire to stay under the limit, even though the breaker is still only 20 amps.
This is exactly the situation real electricians get asked about: "What wire do I need for a 20 amp circuit 200 feet away?" The answer is no longer just "12 gauge."
Wire Size for a 20 Amp Circuit by Run Length
This chart shows the recommended copper wire size for a 20 amp, 120-volt circuit based on the one-way distance from the panel, keeping voltage drop at or under 3%. This is the table almost no competing guide includes.
| One-way run length | Recommended wire | Approx. voltage drop |
|---|---|---|
| Up to 50 ft | 12 AWG | Under 2% |
| 50 – 100 ft | 12 AWG | 2% – 3% |
| 100 – 150 ft | 10 AWG | Under 3% |
| 150 – 200 ft | 10 AWG | Around 3% |
| 200 – 300 ft | 8 AWG | Under 3% |
The exact crossover point depends on the real load on the circuit, not just the breaker size — a circuit pulling the full 20 amps drops more voltage than one pulling 12 amps over the same distance. That's why a calculator that takes your actual amperage and run length beats any fixed chart.
Find your exact wire gauge in seconds
Enter your load, voltage, run length, and allowable voltage drop. Our free wire gauge calculator gives you the correct AWG instantly.
Open the wire gauge calculator →Copper vs Aluminum for 20 Amp Circuits
Everything above assumes copper, which is what nearly all modern branch circuits use. If you're working with aluminum wire — less common indoors — you need to go one gauge thicker because aluminum carries less current per gauge. The aluminum equivalent for a 20 amp circuit is 10 AWG instead of 12 AWG.
Aluminum also requires AL-CU rated terminals and anti-oxidant compound at connections to prevent corrosion. For most residential work, copper is the safer and simpler choice.
The 80% Rule for Continuous Loads
There's one more rule that affects how you use a 20 amp circuit, though not the wire size. For loads running continuously for three hours or more, the NEC says to design for 80% of the breaker's capacity — about 16 amps on a 20 amp circuit. The wire stays 12 AWG, but you shouldn't plan to run the full 20 amps non-stop. This matters for things like EV chargers, space heaters, and workshop equipment.
Frequently Asked Questions
No. 14 AWG is rated for only 15 amps and will overheat on a 20 amp breaker, creating a serious fire risk. It's also a code violation. Always use 12 AWG minimum on a 20 amp circuit.
Upsize to 10 AWG when the one-way run is longer than about 100 feet, to keep voltage drop under 3%. The exact point depends on your actual load — use a wire gauge calculator to be precise.
Yes, using a thicker 10 AWG wire is safe on a 20 amp circuit. It's not always cost-effective for short runs, and the thicker wire can be harder to fit into standard 20 amp devices, but electrically it's fine.
12 AWG copper is rated for 20 amps in standard residential applications, which is why it's the correct match for a 20 amp breaker.
The Bottom Line
For a 20 amp circuit, use 12 AWG copper wire — and never 14 AWG. That covers most standard runs. But the moment your circuit stretches past about 100 feet, voltage drop forces you up to 10 AWG, even though the breaker hasn't changed. Since the real crossover depends on your actual load and distance, run your specific numbers through a wire gauge calculator before you buy wire, and always confirm against your local code or a licensed electrician for any installation.