Wire Gauge (AWG) Calculator

It evaluates its built-in AWG candidates and returns the smallest supported cross-section that meets both the selected ampacity and voltage-drop limits. The ampacity values are a limited NEC Table 310.16 planning model at standard conditions. The separate conductor operating temperature adjusts resistance for the voltage-drop estimate. It does not cover every conductor, terminal, installation method, load characteristic, or local code rule.

Ampacity and voltage drop are separate checks. A conductor may carry the current safely yet have too much resistance over a long run, so meeting your drop limit can require a thicker wire. NEC informational guidance commonly uses 3% for a branch circuit and 5% for feeder plus branch circuit, but the applicable code and equipment requirements control the final design.

This calculator uses VD = 2 x length x current x resistance / 1000 for a single-phase two-wire circuit and VD = sqrt(3) x length x current x resistance / 1000 for a balanced three-phase circuit. Those resistance-only formulas omit reactance, power factor, harmonics, and imbalance, which can matter in real installations.

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.

No. The calculator uses a limited ampacity table and simplified voltage-drop formulas. Real work may require adjustments for ambient temperature, conductor count, continuous loads, terminals, insulation, installation method, fault current, power factor, and local amendments. Have a qualified electrician verify the conductor and protection before installation.