Voltage Drop Calculator

Calculate voltage drop across electrical wire runs based on AWG wire gauge, length, amperage, and copper/aluminum material.

How to use this calculator

1. Select wire gauge.
2. Enter length and load.
3. Check NEC 3% drop rule.

Formula & method

NEC Voltage Drop

VD = (2 × K × I × L) / CM

Single phase drop.

Example

15A 120V over 100ft 12 AWG copper = 2.97V (2.47%).

Key insights

• NEC recommends ≤ 3% drop.

How to interpret your result

% Voltage Drop

Percentage loss.

Frequently asked questions

Why bad?

Causes motor overheating.

Related calculators

• Ohm's Law Calculator — Calculate Voltage, Current, Resistance, or Power (V = I × R, P = V × I).
• Resistor Calculator — Decode 4-band and 5-band resistor color codes to resistance value.

See all other calculators · Explore all online calculators