WireWorks

Wire Size Calculator

Matches a circuit's current draw against the standard copper wire ampacity chart.

Circuit current (A)

Recommended wire gauge

12 AWG

Based on standard 60°C copper wire ampacity — always verify against your local electrical code and the specific run's conditions (length, bundling, ambient temperature).

What you entered

Circuit current (A): 20

1
Match against the standard 60°C copper wire ampacity chart
find smallest wire rated ≥ 20 A= 12 AWG

Result

Recommended wire gauge: 12 AWG

A 20 A circuit needs at least 12 AWG copper wire, per standard 60°C ampacity ratings.

Copper wire gauge by circuit ampacity

Smaller AWG numbers mean thicker wire. These are the common residential copper sizes matched to breaker ratings.

Circuit amps	Copper AWG	Typical circuit
10 A	14	Lighting
15 A	14	General lighting and receptacles
20 A	12	Kitchen and bathroom receptacles
25 A	10	Small appliance
30 A	10	Dryer, water heater, window AC
40 A	8	Range, small subpanel
50 A	6	Range, EV charger
60 A	4	Subpanel
80 A	3	Large subpanel
100 A	1	Service or large subpanel

These assume copper at 60 degrees C in typical residential conditions. Aluminium needs roughly two sizes larger for the same current. Long runs need upsizing for voltage drop even when ampacity is fine, and derating applies where several conductors share a conduit or the ambient temperature is high. Electrical work is life-safety work and is subject to local code and inspection. Use these figures for planning and have a licensed electrician verify anything you intend to build.

This is a starting point, not a final answer

Real wire sizing also depends on wire length (voltage drop over distance), how many wires are bundled together, ambient temperature, and your specific local electrical code — always verify against the National Electrical Code (or your local equivalent) for an actual installation.

Bigger gauge number means thinner wire

AWG (American Wire Gauge) numbering is inverted from what feels intuitive — a 14 AWG wire is thinner and carries less current than a 10 AWG wire. Always double-check you're reading the right direction on a wire gauge chart.

Frequently asked questions

I'm running a 20-amp kitchen circuit — what wire gauge do I need?

12 AWG copper wire, which is rated for 20 amps. 14 AWG is only rated for 15 amps and would be a code violation on a 20-amp breaker. When in doubt, go one gauge thicker (lower number) than the minimum.

What wire size do I need for a 30-amp dryer circuit?

10 AWG copper wire for a 30-amp circuit. This is a 240V circuit, so you'll need 10/3 cable (two hots, one neutral, plus ground) from the panel to the dryer outlet.

Does wire length affect the gauge I need?

Yes — longer runs experience more voltage drop. For runs over 50-75 feet, you may need to go up one wire gauge (thicker wire) to keep voltage drop under 3%. Use the voltage drop calculator to check specific runs.