Breaker Size Calculator
Enter the load in watts and the circuit voltage, and say whether it runs for three hours or more at a time. The calculator gives the current, the breaker size and the minimum copper wire.
- Watts to amps
- 125% continuous rule
- Matching wire gauge
For planning only. Electrical work should be done or checked by a licensed electrician to your local code.
A breaker protects the wire, not the appliance. Its job is to trip before the wire in the wall overheats. That is why the breaker size is chosen from the load, the wire is chosen to carry at least the breaker rating, and a breaker is never swapped for a bigger one just to stop it tripping.
Breaker and wire size chart
Standard breakers with copper wire. Search for a breaker or load.
| Breaker (A) | Copper wire | Max continuous (A) | At 120 V (W) | At 240 V (W) |
|---|---|---|---|---|
| 15 | 14 AWG | 12 | 1440 | 2880 |
| 20 | 12 AWG | 16 | 1920 | 3840 |
| 30 | 10 AWG | 24 | 2880 | 5760 |
| 40 | 8 AWG | 32 | 3840 | 7680 |
| 50 | 6 AWG | 40 | 4800 | 9600 |
| 60 | 6 AWG | 48 | 5760 | 11520 |
| 70 | 4 AWG | 56 | – | 13440 |
| 80 | 4 AWG | 64 | – | 15360 |
| 100 | 3 AWG | 80 | – | 19200 |
Maximum continuous load is 80% of the breaker rating. A 20 A breaker can carry 16 A all day, which is 1,920 W at 120 V.
Load and breaker at two voltages
Continuous loads at 125%. Slide the load.
Large appliances such as ranges, dryers, EV chargers and water heaters run at 240 V because the current is half that at 120 V, which keeps the wire and breaker smaller.
How to size a breaker
From the nameplate to the panel. Step through the method.
Find the load
Read watts on the nameplate. Or amps × volts.
Some appliances, such as air conditioners and heat pumps, list a maximum breaker size on the nameplate. Use that figure where it is given.
Standard, GFCI or AFCI
Size is only part of choosing a breaker. Compare the types.
Trips on overload and short circuit. Used for dedicated appliance circuits.
Also trips on small leaks of current to earth, protecting people from shock.
Also detects arcing from damaged cables and loose connections.
Modern codes require GFCI protection in kitchens, bathrooms, garages and outdoors, and AFCI protection in most living spaces. Dual-function breakers cover both.
Before adding a circuit
Check the panel and the run. Tick each item.
Tick each item as you go.
Your main panel has a total rating, often 100 A or 200 A. Adding a large circuit such as an EV charger may need a load calculation to make sure the service can handle it.
What the result tells you
Breaker, wire and loading. Each tile explains one result.
The next standard rating above the sized current.
Watts divided by volts.
How hard the breaker is working.
Minimum copper for the breaker.
Single for 120 V, double for 208 to 240 V.
Long runs need bigger wire to limit voltage drop. If the circuit runs more than about 50 feet, check the wire size calculator as well.
Frequently Asked Questions
No question matches that search.
What size breaker do I need for 3,600 watts?
At 240 V that is 15 A, or 18.75 A as a continuous load, so a 20 A double pole breaker on 12 AWG wire.
What is the 80% rule for breakers?
A breaker should carry no more than 80% of its rating continuously. It is the same as sizing at 125% of the load.
How many watts can a 20 amp breaker handle?
2,400 W at 120 V peak, or 1,920 W continuous. At 240 V, double those.
What size breaker for a 5,500 W water heater?
5,500 ÷ 240 = 22.9 A. × 1.25 = 28.6 A, so a 30 A breaker with 10 AWG wire.
What size breaker for an EV charger?
A 7.7 kW charger draws 32 A at 240 V, so a 40 A breaker with 8 AWG copper.
Can I replace a 15 A breaker with a 20 A?
Only if the wire is 12 AWG or larger. On 14 AWG wire it is a fire risk.
What is a double pole breaker?
A breaker that takes two slots and connects to both hot legs for 240 V circuits.
Protect the wire, protect the home
Convert the load to amps, apply 125% for anything continuous and round up to the next standard breaker. Match the wire to the breaker and let a licensed electrician check the work before it goes live.
More size calculators
Each one has its own calculator, worked examples and answers to common questions.