Wire Size Calculator

Find the smallest AWG copper or aluminum wire size that meets a required ampacity under NEC Table 310.16.

⏱ Updated: 19 Sep 2026

Calculator

Free wire size calculator: find the smallest AWG copper or aluminum wire size that meets a required ampacity under NEC Table 310.16.

Smallest Compliant Wire Size
AWG
Rated for 0 A at this insulation rating
No standard size in this table reaches that current at this rating. The largest listed size, AWG, tops out at 0 A — a load this size needs parallel conductors or an engineer's sizing beyond this table.

Base NEC Table 310.16 values only — no ambient-temperature or conductor-bundling correction applied. Verify against the current NEC edition before real-world use.

Enter a required current, conductor material, and insulation rating to find the smallest NEC-compliant AWG wire size.

How to Use the Wire Size Calculator

Enter the current the circuit needs to carry, toggle copper or aluminum, and pick the insulation temperature rating — the calculator scans the NEC ampacity table and returns the smallest AWG size whose rating meets or exceeds that current.

This is the Wire Ampacity Calculator run in reverse: instead of starting with a wire size and reading off its rating, you start with a required current and let the tool find the smallest conductor that's actually allowed to carry it.

smallest AWG such that: ampacity(AWG, material, rating) ≥ required current
The same NEC Table 310.16 base values apply here as on the Ampacity calculator — 30°C ambient, no more than 3 current-carrying conductors, no bundling or ambient-temperature correction applied. Treat the result as a starting point for a code-compliant sizing calculation, not a finished spec, and verify against the current NEC edition and any local amendments before wiring anything real.

Worth being clear about what this tool is not: it's not the Wire Gauge Calculator elsewhere on this site, which solves an entirely different problem — given a wire size, it derives resistance and voltage drop from the conductor's physical geometry and the resistivity of copper or aluminum. That's a continuous, formula-based calculation with no code table involved. This one instead answers a code-compliance question — which standard gauge is the smallest one the NEC's ampacity table permits for a given load — and the two calculators can give genuinely different "right answers" for the same circuit, because voltage drop and ampacity are separate constraints that don't always point to the same wire size.

A long run at low current might pass the ampacity check on a small gauge while still failing an acceptable voltage-drop target — exactly the kind of circuit where checking both calculators, not just this one, actually matters.