Find the right AWG wire gauge from load amps, run length, and voltage drop.
Circuit and run
The current the circuit draws, or the breaker it will sit on.
Panel to load, one way. The drop formula doubles it for the return leg.
Two limits, one answer
The gauge has to carry the current and hold the voltage. Short runs are decided by ampacity, long runs by drop, and this page returns the larger of the two.
Estimates only. Not professional advice.
Conductor for this run
6 AWG
Copper at 60°C terminations, carrying 50 A over a 100 ft run at 240 V.
One circuit in free air at 30°C, ungrounded conductors only. More than three conductors in a raceway, a hot ambient, or a separate ground can all change the answer, and the final call belongs to a licensed electrician or your inspector.
Last updated August 5, 2026. Reviewed against NEC 310.16 and 240.4(D) by our expert review team.
One gauge short
Every one of these produces a gauge that looks right on paper. Four of them are about distance, which is the half of wire sizing that gets skipped.
Sizing by amps and stopping there
Ampacity is half the job. A gauge that carries the current all day can still miss the drop target once the run is long enough.
Enter the real one-way distance. 6 AWG holds 3% out to 146 ft at 50 A, and past that the gauge goes up.
Measuring the round trip
The drop formula already multiplies by two for the return leg, so a doubled length is counted twice and the wire comes out a size or two fat.
Measure panel to load, one way, and let the calculator double it.
Reading ampacity off the 90°C column
NEC 110.14(C) holds the whole circuit to the lowest-rated termination, which on residential gear is 60°C or 75°C.
Size from the column your lugs and breaker are stamped for. The 90°C column is for derating math, not for the final pick.
Sizing aluminum like copper
Aluminum carries less current per gauge and loses more voltage over the same distance, so the same load lands on a bigger conductor.
At 50 A over 100 ft this run is 6 AWG in copper and 4 AWG in aluminum. Use AL-rated lugs and antioxidant compound.
Assuming the ground matches the hots
The equipment grounding conductor is sized from the breaker rating per NEC 250.122, not from the conductor you just picked.
Size the ground off the breaker, and increase it proportionally when the hots are upsized for voltage drop.
Sizing for free air when the wire lives in a pipe
This page assumes one circuit in free air at 30°C. A hot attic, or more than three current-carrying conductors in one raceway, cuts the ampacity the table gives you.
Count what shares the raceway and derate before you commit, then check the pipe itself with the conduit fill calculator.
Drop over distance
At 50 A and 240 V, 6 AWG carries the current, but it only holds 3% out to 146 ft. Each bar below is how far that gauge reaches before the drop passes your target, and the vertical rule is your 100 ft run.
6 AWG
55 A
146 ft
2.05% at your run
4 AWG
70 A
233 ft
1.29% at your run
3 AWG
85 A
294 ft
1.02% at your run
2 AWG
95 A
370 ft
0.81% at your run
1 AWG
110 A
467 ft
0.64% at your run
6 AWG leaves 46 ft of headroom before it would need to go up again.
Bars are one-way distances at 240 V and a 3% target. Halve the voltage and every bar halves with it.
Breaker to copper
The pairings most jobs use, with the distance each one reaches at your 3% target and 240 V. A 20 A circuit on 12 AWG copper holds that target for 91 ft before the gauge has to grow.
15 A
14 AWG
76 ft
Lighting, general receptacles
20 A
12 AWG
91 ft
Kitchen, bath, garage, laundry outlets
30 A
10 AWG
97 ft
Electric dryer, water heater, window AC
40 A
8 AWG
115 ft
Electric range, EV charger, larger AC
50 Ayours
6 AWG
146 ft
Range, hot tub, small subpanel
60 A
4 AWG
194 ft
Subpanel, large feeders
100 A
3 AWG
147 ft
100-amp subpanel feeder (copper)
Breaker and wire pairings as this page's own reference table lists them. The branch-circuit rows are the 60°C NM-B figures, the familiar residential chart, while the 100 A feeder row is a 75°C figure, which is how the trade quotes it. The distance column is the same drop arithmetic the calculator runs, at 240 V: at 120 V the same target reaches half as far, because the drop is a percentage of the system voltage.
Copper against aluminum
This is the one real choice on the page. Aluminum carries fewer amps per gauge and loses more volts over the same distance, so the same load lands on a bigger conductor.
Copper
branch circuits
6 AWG
2.05% drop · holds to 146 ft
Outlet, lighting and appliance circuits. More amps per gauge, easy terminations, and the default for wiring inside a house.
your conductor
Aluminum
large feeders
4 AWG
2.12% drop · holds to 142 ft
Service entrances and long subpanel feeders, where cost and weight matter. Size up one to two gauges, use AL-rated lugs and antioxidant compound.
Amps allowed at 60°C
NEC 310.16 at the 60°C column, with 14, 12 and 10 AWG held to the 240.4(D) small-conductor limit. Switch the termination rating in the run options and this table follows it.
Three feeds
Same arithmetic, three distances. The first two are decided by ampacity and the third by the length of the run, which is the whole point of entering it.
20 A · 25 ft · 120 V
12 AWG
20 A breaker · 1.65% drop
Kitchen Receptacle Circuit
A 20 amp small-appliance circuit on a short homerun. Ampacity sets the gauge and the drop never gets near the target.
Decided by ampacity.
50 A · 60 ft · 240 V
6 AWG
50 A breaker · 1.23% drop
Electric Range Circuit
A 240 volt range feed at the far end of a kitchen. The familiar 50 amp pairing, and at this distance the drop never comes into it.
Decided by ampacity.
30 A · 150 ft · 240 V
8 AWG
30 A breaker · 2.93% drop
Detached Garage Well Pump
A pump well past the house. Ampacity alone would allow a smaller conductor, and the distance is what takes it up a size.
Decided by the run length.
All three are copper at 60°C terminations with a 3% target, run through the same function as the readout above.
At the terminals
None of these change the arithmetic. All of them change whether the gauge you buy is the gauge the inspector signs off.
The two in the drop formula is the return leg. Enter the one-way distance from the panel to the load and the calculator handles the round trip.
A load that runs three hours or more is continuous and needs 125 percent of its amps in ampacity. The switch in the run options changes the required ampacity, not the drop.
Terminations decide the column. NEC 110.14(C) ties the circuit to the lowest-rated lug or breaker, so a 90°C conductor on 75°C lugs is a 75°C circuit.
NM-B cable is a 60°C conductor per NEC 334.80, which is why the familiar chart pairs 15 A with 14 AWG and 50 A with 6 AWG. THHN in conduit on 75°C terminals carries more.
Drop is a percentage of system volts, so the same wire and load at 120 V loses twice the percentage it loses at 240 V. Nameplate in watts? Convert it with the amp calculator first.
Upsizing the hots for voltage drop pulls the equipment ground up with them per NEC 250.122, and a fatter bundle needs a bigger raceway.
Two limits
It solves the same problem twice. Once for the current the conductor has to carry, once for the volts it is allowed to lose, and it returns whichever answer is bigger.
required A = load A × 1.25 when continuousdrop V = 2 × K × amps × length ÷ circular milsdrop % = drop V ÷ system volts × 100max run = target % × circular mils × volts ÷ (200 × K × amps)wire = larger of the ampacity and the drop answerThis run, step by step
What sets the gauge
What it does not size
Know the load in watts rather than amps? Convert it with the amp calculator, then size the raceway with the conduit fill calculator.
Before you buy wire
The eight things people ask at the counter, answered against the same tables this page reads.
For a 50-amp circuit, use 6 AWG copper or 4 AWG aluminum at the 75°C column for runs up to roughly 100 feet. Beyond that, check voltage drop. A long 50-amp run may need to step up to 4 AWG copper to stay under 3%. Always confirm your equipment's termination temperature rating.
A 30-amp circuit uses 10 AWG copper (8 AWG aluminum); a 40-amp circuit uses 8 AWG copper (6 AWG aluminum), both at 75°C. These are the ampacity minimums, and long runs for EV chargers or shops often upsize one gauge to limit voltage drop.
A 100-amp feeder typically uses 3 AWG copper or 1 AWG aluminum at 75°C. Many installers run 1 AWG copper or 2/0 aluminum for headroom and easier termination. Subpanel feeders also need a properly sized neutral and a separate equipment grounding conductor per NEC 250.122.
The NEC recommends keeping voltage drop under 3% on a branch circuit (5% total including the feeder). Drop rises with distance and current, so long runs such as detached garages, well pumps and EV chargers 100+ feet out often need a conductor one or two sizes larger than ampacity alone would require. This calculator checks both and gives you the larger.
Copper carries more current per size and terminates easily, so it dominates branch circuits. Aluminum is cheaper and lighter for large feeders and service entrances but needs to be about one to two sizes larger for the same ampacity, uses antioxidant compound, and requires terminals rated for aluminum (AL or CU-AL). For most outlet and appliance circuits, copper is the simpler choice.
Distance doesn't change the ampacity requirement, but it directly increases voltage drop. Doubling the one-way run doubles the drop. A 30-amp circuit might be fine on 10 AWG at 25 feet but need 8 AWG at 120 feet to stay under 3%. Enter your actual one-way run length so the calculator can flag when drop, not ampacity, governs.
The calculator defaults to the 60°C column because the most common residential wire, NM-B cable (Romex), is limited to 60°C ampacity per NEC 334.80, and that is the basis of the familiar chart (15A to 14 AWG, 50A to 6 AWG). Switch to 75°C if you are running THHN/THWN in conduit with 75°C-rated terminals. The 90°C column is only for derating math, not final sizing, because NEC 110.14(C) ties you to the weakest termination's rating. Confirm the rating stamped on your breakers and lugs.
No. The recommended gauge is the ungrounded (hot) conductor. The equipment grounding conductor is sized separately by the breaker rating per NEC 250.122. For example a 20-amp circuit uses a 12 AWG ground and a 60-amp circuit a 10 AWG ground. If you upsize the hots for voltage drop, the ground must be increased proportionally.
Disclaimer
These estimates are for planning purposes only. Actual costs vary by location, material availability, and project complexity. Always get at least 3 local quotes. This calculator does not replace professional advice.
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