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Wire Ampacity Calculator

Look up the rated ampacity of a copper THHN wire gauge (NEC Table 310.16).

Introduction

Wire Ampacity Calculator — Look up the rated ampacity of a copper THHN wire gauge (NEC Table 310.16). Enter Wire gauge to get an instant, accurate result.

Formula

Looks up the rated ampacity of a given copper AWG/kcmil wire size from NEC Table 310.16, 75°C column (THHN/THWN-2 insulation).

Step-by-step

  1. Enter the Wire gauge.
  2. Click Calculate to see your result instantly.

Real-world example

Example: With Wire gauge = 12, the Wire Ampacity Calculator gives Ampacity Amps: 25, Basis: NEC Table 310.16, copper THHN 75°C (differs for aluminum/other insulation ratings).

Frequently Asked Questions

Is this ampacity the same for aluminum wire?
No — aluminum conductors have lower ampacity than copper at the same gauge; this table is copper-only. Aluminum requires a separate NEC Table 310.16 column and is typically upsized versus an equivalent copper circuit.
Does insulation type change the ampacity?
Yes — the 75°C column applies to common insulations like THHN/THWN-2 and XHHW; lower-temperature-rated insulation (like older TW at 60°C) has a lower ampacity for the same conductor size.
What inputs does the Wire Ampacity Calculator need?
You'll need to provide: Wire gauge. All fields use sensible defaults, so you can see a working example immediately and then adjust the values to match your own numbers.
How accurate is the Wire Ampacity Calculator?
The Wire Ampacity Calculator applies the formula exactly as calculated — Looks up the rated ampacity of a given copper AWG/kcmil wire size from NEC Table 310.16, 75°C column (THHN/THWN-2 insulation). — so results are precise for the inputs you provide. Accuracy depends on entering correct, realistic input values.
Is the Wire Ampacity Calculator free to use?
Yes, the Wire Ampacity Calculator is completely free, requires no signup, and runs instantly in your browser.

About the Wire Ampacity Calculator

The Wire Ampacity Calculator uses a real, verifiable formula — Looks up the rated ampacity of a given copper AWG/kcmil wire size from NEC Table 310.16, 75°C column (THHN/THWN-2 insulation). — so results are accurate every time, not an approximation.