Tool · Electrical

Voltage Drop Calculator

Long wire runs lose voltage. Enter the wire size, material, one-way distance, and current to estimate the drop.

Material Wire size (AWG) Current (amps) One-way distance (feet) System voltage Phase

0 V

voltage drop

drop %

0 V

voltage at load

Estimate only. This uses approximate DC conductor resistance and does not replace proper engineering. Wire sizing also depends on ampacity, temperature rating, conduit fill, and breaker size. Always follow the NEC and your local code, and work with a licensed electrician.

How it works

Voltage drop = factor × resistance × distance × current. Current travels out and back, so single-phase uses a factor of 2; three-phase uses √3 (≈ 1.732).

A common guideline is to keep voltage drop under 3% on a branch circuit (5% total including the feeder).

Related: Ohm's law calculator →