Wire Gauge Calculator
A general reference for typical copper wire gauge by circuit amperage. This is a simplified lookup, not an electrical code determination — read the note below before using it for any real wiring work.
Read this before using the result
This calculator is a simplified reference table, not a wire sizing calculation. Real wire sizing accounts for the specific circuit's ampacity requirements, run length, ambient temperature, how many conductors share a conduit, and local code amendments — none of which this tool measures. Treat the result as a starting point for a conversation with a licensed electrician, not a final answer.
How this reference works
The gauge shown comes from a standard copper wire table matched to common circuit amperages:
15 A → 14 AWG 20 A → 12 AWG 30 A → 10 AWG 40 A → 8 AWG 50 A → 6 AWG
If the run is longer than 100 feet, the calculator flags that voltage drop becomes a more significant concern and suggests checking whether the next larger gauge is warranted — this is a general rule of thumb, not a calculated voltage-drop percentage for your specific circuit.
Worked example
A 20 A circuit, 120 V, running 80 feet one-way:
- 20 A maps to 12 AWG in the reference table.
- 80 ft is under the 100 ft threshold, so no upsizing flag appears.
- Still confirm this against local code and, ideally, a licensed electrician before wiring the circuit.
Copper vs aluminum
Copper is the more common choice in residential wiring and generally needs a smaller gauge than aluminum for the same ampacity. Aluminum wiring requires a larger gauge to carry the same current safely, and has specific installation requirements — including approved connectors and antioxidant compound — to prevent loose-connection problems over time. This calculator's table assumes copper; aluminum sizing is different and outside the scope of this simplified reference.
Frequently asked questions
What gauge wire do I need for a 20A circuit?
12 AWG copper wire is the commonly used size for a standard 20 amp circuit. This is a general reference figure — always confirm against your local electrical code and the specific installation before wiring any circuit.
Does wire run length actually matter?
Yes. Longer runs experience more voltage drop, which can cause dimming, reduced appliance performance, or overheating on marginal circuits. A run beyond roughly 100 feet often benefits from upsizing to the next larger gauge, though the exact point depends on the actual current, voltage and acceptable drop.
Copper vs aluminum wiring — what's the difference?
Copper generally needs a smaller gauge than aluminum for the same ampacity. Aluminum requires a larger gauge and has specific installation requirements to prevent connection problems over time, so confirm which material a circuit uses before assuming standard copper gauge sizes apply.
When do I need a permit or a licensed electrician?
Most jurisdictions require a permit and licensed electrician for new circuits, panel work, or anything beyond simple like-for-like fixture replacement. Requirements vary significantly by location — check with your local building department, and hire a licensed electrician for anything you're not fully confident in.