Tech
Wire Gauge (AWG) Calculator
Find the smallest AWG conductor that meets NEC ampacity and your voltage-drop limit. Copper or aluminum, single- or three-phase, 60/75/90 C insulation.
Wire gauge (AWG) calculator
A
Continuous current the conductors will carry.
ft
Distance from panel to load. Round-trip is doubled internally.
V
Common: 12 V (auto, RV), 120 V (US branch), 240 V (US dryer/HVAC), 480 V (commercial).
%
NEC recommends 3% per branch, 5% total feeder + branch.
Recommended wire
AWG 12
Smallest gauge that meets both the NEC ampacity and your voltage-drop limit.
Voltage drop
3.18 V
Voltage drop
2.65 %
Ampacity
25 A
R per 1000 ft
1.588 Ω
Power loss
63.52 W
| Option | AWG | Drop (V) | Drop (%) | Ampacity | Status |
|---|---|---|---|---|---|
| One size up (oversized) | AWG 10 | 2 | 1.67 | 35 A | Meets both |
| One size down (marginal) | AWG 14 | 5.05 | 4.21 | 20 A | Over voltage drop |
Frequently Asked Questions about the Wire Gauge (AWG) Calculator
How does this calculator pick a wire size?
It walks the AWG table from thinnest to thickest and returns the first gauge that satisfies two constraints at the same time: NEC ampacity for your insulation temperature rating must be at least the load current, and the round-trip voltage drop must stay under your allowed percentage. That is the standard residential and light-commercial sizing rule.
Why does the voltage-drop limit force me to a larger wire than the ampacity table suggests?
Ampacity sizing assumes a short run from the panel to the load. On long runs the conductor's own resistance burns enough voltage that the load no longer sees its rated supply, so you have to step up to a thicker wire. The NEC recommends keeping branch-circuit drop under 3% and total feeder-plus-branch drop under 5%.
What is the difference between single-phase and three-phase voltage drop?
A single-phase 2-wire circuit uses the formula VD = 2 x run_length x I x R / 1000 because current flows out on the hot leg and back on the neutral. A balanced three-phase circuit uses VD = sqrt(3) x run_length x I x R / 1000 because the three-phase math collapses one of the round-trip legs. For the same load and gauge, three-phase drop is about 87% of single-phase.
Why does aluminum need a thicker wire than copper for the same load?
Aluminum's resistivity is roughly 1.6 times copper's (16.94 vs 10.371 Ohm cmil/ft at 20 C), so the same AWG aluminum conductor has about 60% more resistance per foot. To keep voltage drop under the same percentage limit you usually step up one or two gauges, and you must also use connectors and lugs rated for aluminum.
Does this replace a licensed electrician for sizing a real circuit?
No. The calculator uses NEC Table 310.16 ampacities for three current-carrying conductors in a raceway at standard ambient temperature; real installations may need derating for conduit fill, ambient heat, bundling, continuous loads, or local amendments. Use it for first-pass planning and have a licensed electrician verify the final design.