---
title: "Wire gauge and voltage drop — free, runs in your browser"
description: "AWG to mm², current capacity and voltage drop over a run. Free, no sign-up, and nothing you enter leaves your browser."
url: https://atoneplace.net/tools/wire-gauge-calculator/
site: "At One Place"
---

# Wire gauge and voltage drop

AWG to mm², current capacity and voltage drop over a run.

## How it works

Converts between AWG and square millimetres, and calculates voltage drop for a given current, length and conductor size.

The AWG scale runs backwards — a larger number is a thinner wire — because it originally counted how many times the wire was drawn through successively smaller dies. Every six gauge steps roughly halves the diameter, and every three steps roughly halves the cross-sectional area.

Voltage drop is the reason long runs need thicker cable than the current alone suggests. The usual working limit is 3% for a branch circuit and 5% overall; beyond that, motors run hot, lights dim and heaters underperform. The drop is proportional to length, so doubling the run doubles it.

These figures are for copper at ordinary temperatures. Aluminium has roughly 60% of copper’s conductivity and needs about two gauge sizes larger for the same performance. Anything permanent must follow the wiring regulations that apply where you are, which take account of grouping, insulation, ambient temperature and installation method — none of which a simple calculator can see.

> This tool runs entirely in your browser. Nothing you enter is sent to a server, logged or stored, and the page keeps working with the network disconnected.

## Common questions

### Why is a higher AWG number a thinner wire?

The scale counts drawing passes through progressively smaller dies. More passes means thinner wire, so the number goes up as the size goes down.

### What voltage drop is acceptable?

Conventionally 3% on a branch circuit and 5% total. Beyond that, motors heat, lights dim and heating elements underperform.

### Can I use aluminium instead of copper?

Only with the right terminations, and you need about two gauge sizes larger — aluminium has roughly 60% of copper’s conductivity.

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## Sources

- Typical range compiled from manufacturer specifications — At One Place (/about/)