Choose a wire gauge and material, then enter current, length, and voltage to find resistance and voltage drop.

How to Use the Wire Gauge Calculator

Choose a standard AWG size from the dropdown, toggle copper or aluminum, then fill in current, one-way run length, and system voltage. Every field feeds straight into the resistance and voltage-drop figures below — change any one and the results update immediately.

The #2 Gauge Wire Calculator and the AWG to mm Calculator on this site both stop short of what a working electrician actually wants: total wire resistance for a real run. This tool goes there, and it does it differently from a NEC-table lookup — it derives resistance from the wire's own physical geometry and the resistivity of the metal itself, the same first-principles approach an engineer reaches for when sanity-checking a published table rather than trusting it blindly.

Diameter (mm) = 0.127 × 92^((36 − AWG) ÷ 39)
Resistance per meter = Resistivity ÷ Cross-Sectional Area
Total Resistance = Resistance per meter × Length (m) × 2
Voltage Drop = Total Resistance × Current

Copper's resistivity sits at about 1.724 × 10⁻⁸ Ω·m, aluminum's at roughly 2.65 × 10⁻⁸ Ω·m — both standard handbook values at room temperature. Divide either by a wire's cross-sectional area (itself derived from the AWG formula) and the result is resistance per unit length. Multiply by the round-trip distance and by the current, and voltage drop falls out the other end.

What this calculator doesn't do, on purpose: apply a temperature correction. Real wire runs hotter in service — 75-90°C is typical for a loaded conductor — and resistance climbs with temperature for any metal, so the number here is a room-temperature baseline, not the exact figure you'd measure on a hot circuit. A proper code-compliance voltage-drop calculation also has to account for inductive reactance on AC circuits above a certain conductor size, which this simplified DC-resistance model skips entirely. Treat the output as a solid engineering estimate, not a substitute for a full ampacity and voltage-drop study on anything safety-critical.