Voltage Drop Calculator

Calculate electrical voltage loss over distance per NEC guidelines.

Phase

Wire Material

Wire Gauge (AWG)

Source Voltage

Supply voltage at the source (e.g., 120V, 240V, 480V).

Load Current

Current draw of the load in Amperes.

One-Way Length

One-way cable run distance.

Unit

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Voltage Drop

—V

Percent Drop

—%

End Voltage

— V

Wire Resistance

— Ω

Documentation

How It Works

Voltage drop occurs when electrical current flows through a wire. The wire's resistance converts some electrical energy to heat, reducing the voltage available at the load end.

NEC (National Electrical Code) recommends a maximum 3% voltage drop for branch circuits and 5% total (feeder + branch combined) to ensure proper equipment operation and efficiency.

Formulas

Single-phase (multiply is ×2)
Three-phase uses √3 instead of 2

Last Updated: February 28, 2026

Disclaimer: For estimation purposes only. Always consult a licensed electrician and follow local electrical codes.

Frequently Asked Questions