ElectricalCharts

Wire Size Chart

Breaker rating to conductor size for copper and aluminium, plus the circuits each size normally serves.

Quick answer

At 75 °C terminations: 15 A → 14 AWG copper, 20 A → 12 AWG, 30 A → 10 AWG, 40 A → 8 AWG, 50 A → 6 AWG, 60 A → 4 AWG, 100 A → 3 AWG, 200 A → 250 kcmil. Aluminium runs one to two sizes larger. Long runs and continuous loads both push the conductor up from these minimums.

Wire size by breaker rating

Smallest conductor whose estimated 75 °C ampacity covers the device rating, at 30 °C ambient with no more than three current-carrying conductors.

BreakerCopperAluminiumMax continuous load (80%)
15 A14 AWG12 AWG12 A
20 A12 AWG10 AWG16 A
25 A10 AWG10 AWG20 A
30 A10 AWG8 AWG24 A
35 A8 AWG6 AWG28 A
40 A8 AWG6 AWG32 A
45 A6 AWG6 AWG36 A
50 A6 AWG4 AWG40 A
60 A4 AWG4 AWG48 A
70 A4 AWG3 AWG56 A
80 A4 AWG2 AWG64 A
90 A3 AWG1 AWG72 A
100 A2 AWG1/0 AWG80 A
110 A1 AWG1/0 AWG88 A
125 A1 AWG2/0 AWG100 A
150 A2/0 AWG3/0 AWG120 A
175 A3/0 AWG4/0 AWG140 A
200 A4/0 AWG250 kcmil160 A
225 A4/0 AWG300 kcmil180 A
250 A250 kcmil400 kcmil200 A
300 A350 kcmil500 kcmil240 A
350 A500 kcmil600 kcmil280 A
400 A500 kcmil750 kcmil320 A
Formula estimate — source: Site ampacity model at 75 °C terminations

Source & method: Terminations are the usual limit: most breakers and lugs above 100 A are rated 75 °C even on 90 °C wire.

Wire size by circuit and appliance

CircuitBreakerVoltageCopperAluminiumNotes
Lighting circuit15 A120 V14 AWG12 AWGStandard residential lighting branch
General receptacles20 A120 V12 AWG10 AWGKitchen and garage small appliance
Bathroom receptacles20 A120 V12 AWG10 AWGDedicated GFCI circuit
Dishwasher / disposal20 A120 V12 AWG10 AWGOften on its own circuit
Microwave20 A120 V12 AWG10 AWGDedicated circuit for built-in units
Window air conditioner20 A120 V12 AWG10 AWGCheck nameplate before sizing
Water heater30 A240 V10 AWG8 AWG4500 W element typical
Electric dryer30 A240 V10 AWG8 AWGFour-wire receptacle
EV charger (Level 2, 24 A)30 A240 V10 AWG8 AWGContinuous load — 125% applies
Electric range / oven40 A240 V8 AWG6 AWG50 A common on larger ranges
EV charger (Level 2, 40 A)50 A240 V6 AWG4 AWGContinuous load — 125% applies
Hot tub / spa panel50 A240 V6 AWG4 AWGGFCI protection required
Sub-panel, small shop60 A240 V4 AWG4 AWGFeeder to detached structure
Sub-panel, garage / shop100 A240 V2 AWG1/0 AWGCommon detached-garage feeder
Service / main feeder200 A240 V4/0 AWG250 kcmilTypical modern residential service
Typical circuits. Always size to the actual equipment nameplate, not the category.

When length forces a bigger wire

Ampacity gives the floor. On any run over about 100 feet, voltage drop usually decides the size. A 20 A load at 120 V on 12 AWG copper exceeds 3% drop past roughly 60 feet one-way, so a long garage or outbuilding circuit lands on 10 or 8 AWG even though 12 AWG is "big enough" for the breaker.

14 AWG18 A copper · 0.0641" dia · full spec sheet12 AWG24 A copper · 0.0808" dia · full spec sheet10 AWG32 A copper · 0.1019" dia · full spec sheet8 AWG44 A copper · 0.1285" dia · full spec sheet6 AWG59 A copper · 0.1620" dia · full spec sheet4 AWG80 A copper · 0.2043" dia · full spec sheet

Run your actual length through the voltage drop calculator

Frequently asked

What size wire do I need for a 20 amp circuit?
12 AWG copper is the standard conductor for a 20 A branch circuit. 10 AWG aluminium is the usual equivalent. On runs beyond roughly 100 feet at 120 V, voltage drop often pushes the copper up to 10 AWG.
What size wire for a 50 amp circuit?
6 AWG copper covers a 50 A circuit at 75 °C terminations; 4 AWG aluminium is the usual equivalent. For a 50 A continuous load such as an EV charger, size the conductor for the 125% design current, not the raw load.
What size wire for a 100 amp sub-panel?
3 AWG copper or 1 AWG aluminium is the common choice for a 100 A feeder at 75 °C. Long feeders to a detached building frequently need one or two sizes larger to keep total voltage drop under 5%.
Can I use a smaller wire if the run is short?
No. Ampacity sets the minimum size regardless of length; a short run cannot go below it. Length only ever pushes the conductor larger, never smaller.
Should I use copper or aluminium?
Aluminium is cheaper per amp and dominates service entrance and feeder work, but needs one to two sizes larger, listed AL-rated terminations and anti-oxidant compound. Copper is standard for branch circuits and small runs.

Gear for branch-circuit work

Gear for branch-circuit work

Tools that pair with these circuit sizes.

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