Wire Size Calculator
The smallest standard gauge that carries the current and holds the voltage drop.
What is Wire Size?
A conductor has to satisfy two limits that disagree constantly. Ampacity asks whether it will get too hot; voltage drop asks whether the load will still see enough volts at the far end. A 20 A load over 3 m is fine on 12 AWG by ampacity, and the same load over 30 m needs 8 AWG or better because the drop is over the limit. Both are computed here, and the binding one is named.
How it works
Conductor resistance is the material's resistivity divided by the cross-sectional area, taken from the standard AWG diameters, and the drop is twice the current times that resistance times the one-way length — the factor of two is the return conductor, which is the half of the circuit people forget. Every gauge in the table is evaluated against the ampacity column for the chosen installation and the drop limit; the thinnest gauge that passes both is the answer, and the table shows why each thinner one failed. Ampacity ratings are installation dependent, which is why the installation is a selector rather than an assumption.
- Enter your input. Type or paste your input into the field above — the tool responds instantly.
- Review the result. Output updates live as you type. Everything runs entirely in your browser.
- Copy or download. Use the Copy button to grab the result, or Download to save it as a file.
Examples
Realistic sample
Type or paste any realistic input — the tool computes the result locally and instantly.
Common mistakes
Expecting a server round-trip
Nothing is uploaded — every tool in this category runs entirely in your browser.