Voltage Drop & Wire Gauge (AWG) Calculator
Calculate voltage drop over a copper or aluminum cable run by AWG size, current and length — and find the smallest wire gauge that keeps the drop under 3%.
How to use
- 1Enter the voltage, current, one-way length and wire material.
- 2Pick a gauge to check, or read the suggested gauge for a 3% drop.
How it's calculated
Resistance = ρ × length ÷ area. Voltage drop = 2 × I × R_one-way for single-phase/DC (√3 × I × R for three-phase). AWG diameter = 0.127 mm × 92^((36 − n) ÷ 39).
Frequently asked questions
What voltage drop is acceptable?
The NEC recommends (in an informational note) no more than 3% on a branch circuit and 5% overall.
Is voltage drop the same as ampacity?
No — ampacity is how much current a wire can safely carry without overheating. Check both; the minimum ampacity column shows NEC 75 °C copper ratings.
Should I trust this for electrical work?
Use it for planning. Wiring must follow your local electrical code, and a licensed electrician should verify permanent installations.