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.
| Breaker | Copper | Aluminium | Max continuous load (80%) |
|---|---|---|---|
| 15 A | 14 AWG | 12 AWG | 12 A |
| 20 A | 12 AWG | 10 AWG | 16 A |
| 25 A | 10 AWG | 10 AWG | 20 A |
| 30 A | 10 AWG | 8 AWG | 24 A |
| 35 A | 8 AWG | 6 AWG | 28 A |
| 40 A | 8 AWG | 6 AWG | 32 A |
| 45 A | 6 AWG | 6 AWG | 36 A |
| 50 A | 6 AWG | 4 AWG | 40 A |
| 60 A | 4 AWG | 4 AWG | 48 A |
| 70 A | 4 AWG | 3 AWG | 56 A |
| 80 A | 4 AWG | 2 AWG | 64 A |
| 90 A | 3 AWG | 1 AWG | 72 A |
| 100 A | 2 AWG | 1/0 AWG | 80 A |
| 110 A | 1 AWG | 1/0 AWG | 88 A |
| 125 A | 1 AWG | 2/0 AWG | 100 A |
| 150 A | 2/0 AWG | 3/0 AWG | 120 A |
| 175 A | 3/0 AWG | 4/0 AWG | 140 A |
| 200 A | 4/0 AWG | 250 kcmil | 160 A |
| 225 A | 4/0 AWG | 300 kcmil | 180 A |
| 250 A | 250 kcmil | 400 kcmil | 200 A |
| 300 A | 350 kcmil | 500 kcmil | 240 A |
| 350 A | 500 kcmil | 600 kcmil | 280 A |
| 400 A | 500 kcmil | 750 kcmil | 320 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
| Circuit | Breaker | Voltage | Copper | Aluminium | Notes |
|---|---|---|---|---|---|
| Lighting circuit | 15 A | 120 V | 14 AWG | 12 AWG | Standard residential lighting branch |
| General receptacles | 20 A | 120 V | 12 AWG | 10 AWG | Kitchen and garage small appliance |
| Bathroom receptacles | 20 A | 120 V | 12 AWG | 10 AWG | Dedicated GFCI circuit |
| Dishwasher / disposal | 20 A | 120 V | 12 AWG | 10 AWG | Often on its own circuit |
| Microwave | 20 A | 120 V | 12 AWG | 10 AWG | Dedicated circuit for built-in units |
| Window air conditioner | 20 A | 120 V | 12 AWG | 10 AWG | Check nameplate before sizing |
| Water heater | 30 A | 240 V | 10 AWG | 8 AWG | 4500 W element typical |
| Electric dryer | 30 A | 240 V | 10 AWG | 8 AWG | Four-wire receptacle |
| EV charger (Level 2, 24 A) | 30 A | 240 V | 10 AWG | 8 AWG | Continuous load — 125% applies |
| Electric range / oven | 40 A | 240 V | 8 AWG | 6 AWG | 50 A common on larger ranges |
| EV charger (Level 2, 40 A) | 50 A | 240 V | 6 AWG | 4 AWG | Continuous load — 125% applies |
| Hot tub / spa panel | 50 A | 240 V | 6 AWG | 4 AWG | GFCI protection required |
| Sub-panel, small shop | 60 A | 240 V | 4 AWG | 4 AWG | Feeder to detached structure |
| Sub-panel, garage / shop | 100 A | 240 V | 2 AWG | 1/0 AWG | Common detached-garage feeder |
| Service / main feeder | 200 A | 240 V | 4/0 AWG | 250 kcmil | Typical modern residential service |
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.
Wire size by breaker rating
A dedicated page for every standard overcurrent device rating, with copper and aluminium sizes, derating and run lengths.
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.
Related charts & calculators
- Ampacity ChartEstimated allowable ampacity by conductor size, material and insulation rating.
- Wire Gauge ChartAWG diameter, circular mils, resistance and amp capacity in one table.
- kcmil Wire Size ChartMCM to AWG conversion, circular mils, resistance and ampacity for 250-750 kcmil.
- Conduit Fill ChartMaximum THHN conductors per trade size for every raceway type.
- EMT Conduit Fill ChartConductor counts and internal areas for electrical metallic tubing.
- PVC Conduit Fill ChartSchedule 40 and Schedule 80 conductor counts and usable areas.