20 Amp Wire Size
Find the copper or aluminum wire for a 20 A breaker, check the voltage drop for your run, and see how far the size can go.
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Assumes NEC 2023 Table 310.16: copper or aluminum, up to 3 current-carrying conductors in a raceway or cable, 30 °C ambient, 60 °C terminals for a 20 A circuit (110.14(C)), 14 AWG limited to 15 A (240.4(D)), 3 % drop target; ground wire not included. Runs in your browser. Verify with your local code and a licensed electrician before you install.
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How to use the 20 Amp Wire Size Calculator
- Keep 20 in “Breaker rating (A)”, or type the rating of your breaker.
- Enter the nameplate or calculated current in “Load current (A)”. Leave it empty to size for the full 20 A, which is the safe choice when you do not know the load.
- Tick “Continuous load (3 hours or more)” for an EV charger, a heater or another long-running load. The design current becomes 125 % of the load and must stay at or under 20 A.
- Pick the “Supply type” and enter “Voltage (V)”: 120 for a general outlet, or 240 for a 240 V load. For three phase, use the line-to-line voltage.
- Type the “One-way length” in ft or m, measured along the cable or conduit route from the panel to the load.
- Choose Copper or Aluminum under “Conductor” and the “Insulation temperature rating” printed on the cable, for example 90 °C for THWN-2 in conduit (the terminal setting still caps the answer at the 60 or 75 °C column).
- Leave “Allowed voltage drop (%)” at 3 unless your project sets another limit.
- Open the advanced settings only when they apply: “Terminal temperature rating” (set 75 °C only when the breaker and the equipment lugs are listed for it), “Ambient temperature” and the number of current-carrying conductors.
- Read “Recommended wire size”, “Deciding limit” and “Longest run of the recommended size”, then the steps and warnings.
The example buttons load a general outlet, an EV charger, a window or mini-split AC, a long 120 V run and an aluminum circuit.
What size wire do I need for a 20 amp breaker?
A 20 A breaker needs a conductor whose allowed ampacity reaches 20 A. With Auto terminals (60 °C for circuits up to 100 A, NEC 110.14(C)(1)) that is 12 AWG copper, which is allowed 20 A on a 20 A breaker, or 10 AWG aluminum. 14 AWG is limited to 15 A (NEC 240.4(D)), so it is never used on a 20 A breaker, even for a short run.
| Settings (20 A breaker, Auto terminals) | Copper | Aluminum |
|---|---|---|
| Breaker-protected size (60 °C terminals) | 12 AWG | 10 AWG |
The ground wire is separate. For a 20 A breaker the equipment grounding conductor is 12 AWG copper or 10 AWG aluminum (NEC Table 250.122), found with the equipment grounding conductor calculator.
How far can you run 20 amp wire?
At 16 A on 120 V, 12 AWG copper keeps the drop under 3 % up to about 57 ft one way. Past that the calculator moves up a size.
| Copper unless noted | One-way length | Result |
|---|---|---|
| 16 A load, 120 V | 50 ft | 12 AWG, 2.63 % drop |
| 16 A load, 120 V | 75 ft | 10 AWG, 2.48 % drop |
| 16 A load, 120 V | 100 ft | 8 AWG, 2.08 % drop |
| 16 A load, 120 V | 150 ft | 6 AWG, 1.96 % drop |
| 16 A load, 120 V | 200 ft | 6 AWG, 2.61 % drop |
| 20 A load, 120 V | 30 ft | 12 AWG, 1.97 % drop |
| 16 A load, 240 V | 40 ft | 12 AWG, 1.05 % drop |
| 16 A load, 240 V | 100 ft | 12 AWG, 2.63 % drop |
| 16 A load, 240 V | 150 ft | 10 AWG, 2.48 % drop |
| 16 A load, aluminum, 120 V | 75 ft | 8 AWG, 2.57 % drop |
What about a continuous load on a 20 amp circuit?
A continuous load is sized at 125 %. A 16 A continuous load has a design current of 20 A, so it still fits 12 AWG copper on a 20 A breaker (240 V, 50 ft: 1.31 % drop). A continuous 20 A load has a design current of 25 A, which needs 10 AWG, but 25 A is more than the 20 A breaker, so the load must be reduced or the breaker enlarged.
Worked examples
| Input | Result |
|---|---|
| 20 A breaker, 16 A load, 120 V, 50 ft, copper 75 °C | 12 AWG (2.63 %) |
| 20 A breaker, 20 A load, 120 V, 30 ft, copper 75 °C | 12 AWG (1.97 %) |
| 20 A breaker, 16 A load, 240 V, 40 ft, copper 75 °C | 12 AWG (1.05 %) |
| 20 A breaker, 16 A load, 120 V, 150 ft, copper 75 °C | 6 AWG (1.96 %) |
| 20 A breaker, 16 A load, 120 V, 75 ft, aluminum 75 °C | 8 AWG (2.57 %) |
Calculated by the tool above; open it with the same values to see each step.
Questions, briefly answered
What size wire for a 20 amp breaker?
12 AWG copper or 10 AWG aluminum with Auto terminals. Use the 60 °C column for circuits of 100 A or less unless the breaker and equipment are listed for 75 °C.
Is 12 gauge right for 20 amps?
Yes, for a 20 A breaker. 12 AWG copper is allowed 20 A. At 16 A on 120 V over 50 ft the drop is 2.63 %, inside the 3 % target.
Can I use 14 gauge wire on a 20 amp circuit?
No. 14 AWG is limited to 15 A (NEC 240.4(D)), so it cannot be protected by a 20 A breaker. Use 12 AWG copper.
Is 20 amp aluminum wire 10 AWG?
Yes, 10 AWG aluminum with Auto terminals. Aluminum needs lugs marked AL/CU, and the tool shows the copper size next to it.
How far can 12 AWG run on a 20 amp circuit?
At 16 A on 120 V, about 57 ft one way keeps the drop at 3 % or under. At 75 ft the answer moves to 10 AWG (2.48 %).
What wire do I need for a 20 amp EV charger or mini-split?
A 16 A continuous load on a 20 A breaker needs 12 AWG copper (240 V, 50 ft gives 1.31 %). For a window or mini-split AC, enter the unit’s nameplate current as the load and your run length; the result gives the size, the drop and the longest run.
What size ground wire for a 20 amp breaker?
12 AWG copper or 10 AWG aluminum under NEC Table 250.122. It is not included in the wire size above.