Voltage Drop Calculator

Calculate electrical voltage loss over distance per NEC guidelines.

V
Supply voltage at the source (e.g., 120V, 240V, 480V).
A
Current draw of the load in Amperes.
One-way cable run distance.

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

Loading formula…
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
How to Use

About the Voltage Drop Calculator

What it calculates

This voltage drop calculator computes engineering and applied physics quantities for circuits, fluids, and mechanical systems. Calculate electrical voltage loss over distance per NEC guidelines.

When to use it

Use for coursework, lab estimates, and quick technical calculations.

Example

Adjust the inputs above to model your specific scenario with the Voltage Drop Calculator.

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