What Size Breaker Do I Need?

Find the correct circuit breaker size and wire gauge for any appliance or electrical load. Select from 40+ common appliances — including hot tubs, EV chargers, dryers, and welders — or enter your own values. Results follow NEC requirements including the 125% continuous load rule.

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Recommended Breaker & Wire

Select an appliance or enter custom values to see results.

How to Determine the Right Breaker Size: Step-by-Step

Choosing the correct circuit breaker size protects your wiring and equipment from overloads. Here is the process for selecting the right breaker for any load.

Step 1: Find the Nameplate Amps or Calculate From Watts

Check the appliance nameplate for the amperage rating. If only watts and voltage are listed, divide watts by voltage: Amps = Watts / Volts. A 4,800W water heater on 240V draws 20 amps.

Step 2: Apply 125% for Continuous Loads

If the load runs for 3 or more hours continuously (water heaters, baseboard heaters, EV chargers), multiply the amps by 1.25 per NEC 210.20. A 20A continuous load requires 25A breaker capacity.

Step 3: Select the Next Standard Breaker Size

Standard breaker sizes are 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, and 100 amps. Choose the next size equal to or greater than your calculated load. For 25A calculated, select a 30A breaker.

Step 4: Match the Wire Gauge

Every breaker size requires a minimum wire gauge: 15A = #14 AWG, 20A = #12, 30A = #10, 40A = #8, 50A = #6, 60A = #6 or #4. The wire must be rated for the breaker, not just the actual load.

Step 5: Check GFCI and AFCI Requirements

Kitchens, bathrooms, outdoors, garages, and basements require GFCI protection. Bedrooms, living rooms, and most habitable rooms require AFCI protection. Some locations require dual-function AFCI/GFCI breakers.

Formula

Required Breaker Amps = Load Amps x 1.25 (if continuous)

Where: Load Amps = Watts / Voltage, 1.25 = NEC continuous load multiplier (loads running 3+ hours). Select the next standard breaker size above the calculated value

Worked Example

Scenario: Determine the breaker size for a 4,800W, 240V electric water heater (continuous load).

  • Step 1: Amps = 4,800W / 240V = 20A
  • Step 2: Continuous load: 20A x 1.25 = 25A
  • Step 3: Next standard size above 25A = 30A breaker
  • Step 4: 30A breaker requires #10 AWG copper wire minimum
  • Step 5: Water heaters do not require GFCI unless within 6 feet of a sink (check local codes)

Result: Use a 30A double-pole breaker with #10 AWG copper wire for the 4,800W water heater.

Common Breaker Sizes & Wire Gauges

Quick reference for standard residential breaker sizes, minimum wire gauges (copper, THHN/THWN at 75°C), and typical appliances on each circuit. Always verify with the appliance nameplate and local codes.

BreakerWire (Cu)VoltageCommon Uses
15A14 AWG120VGeneral lighting, bedrooms, living rooms
20A12 AWG120VKitchen outlets, bathrooms, garage, outdoor, laundry
20A12 AWG240VSmall window AC, EV charger (16A), baseboard heaters
30A10 AWG240VElectric dryer, water heater, small AC, EV charger (24A)
40A8 AWG240VElectric range/oven, EV charger (32A), large AC unit
50A6 AWG240VElectric range, EV charger (40A), hot tub, sub-panel
60A6 AWG240VEV charger (48A), hot tub, large welder, sub-panel
100A1 AWG240VSub-panel feed, large electric furnace

Frequently Asked Questions

What size breaker do I need for a hot tub?

Most hot tubs require a 50A or 60A, 240V GFCI breaker with 6-gauge copper wire. Check your hot tub's nameplate — it will list the exact amperage and voltage requirements. NEC requires GFCI protection and a disconnect switch within sight of the hot tub, located at least 5 feet from the water's edge. A licensed electrician should install the circuit.

What size breaker do I need for an EV charger?

It depends on the charger's amperage. Because EV charging is a continuous load, you must apply the NEC 125% rule: a 40A charger needs a 50A breaker, a 48A charger needs a 60A breaker, and a 32A charger needs a 40A breaker. Most homeowners install a 40A or 48A Level 2 charger, requiring a 50A or 60A breaker with 6-gauge copper wire.

What size breaker do I need for an electric dryer?

A standard residential electric dryer uses a 30A, 240V breaker with 10-gauge copper wire. The outlet is typically a NEMA 14-30 (4-prong) receptacle. Older homes may have a 3-prong NEMA 10-30 outlet. If your dryer nameplate shows more than 24A, you may need a larger breaker — always check the manufacturer's requirements.

What is the NEC 125% rule for continuous loads?

Per NEC 210.20(A), if an appliance runs continuously for 3 hours or more (like an EV charger, space heater, pool pump, or baseboard heater), the circuit breaker must be rated at 125% of the load current. For example, a 40A EV charger requires a breaker rated at least 40 x 1.25 = 50A. This prevents the breaker from overheating during extended operation.

What size breaker for a welder?

Small hobby welders (120V) typically need a 30A circuit. Larger 240V welders need 40-60A breakers depending on their rated input current. Check the welder's nameplate for the maximum input amperage and size the breaker accordingly. Welders are generally not continuous loads since they cycle on and off, so the 125% rule usually doesn't apply.

Can I use a larger breaker than recommended?

No — never install a breaker larger than what the wire can safely carry. The breaker protects the wire from overheating. A 15A breaker protects 14 AWG wire, a 20A breaker protects 12 AWG wire, etc. Using an oversized breaker is a fire hazard. If you're tripping a breaker, the solution is to reduce the load or install a new circuit with larger wire and an appropriately sized breaker.

When is a GFCI breaker required?

NEC requires GFCI protection for circuits in bathrooms, kitchens (within 6 feet of a sink), garages, outdoors, basements, crawl spaces, laundry areas, and near pools, hot tubs, and spas. GFCI breakers protect against electric shock by detecting current leaks. For 240V circuits like hot tubs, a GFCI breaker is used instead of a GFCI outlet.

What size breaker for a window air conditioner?

Most small window AC units (5,000-8,000 BTU) run on a standard 120V, 15-20A circuit. Larger units (12,000+ BTU) may require a dedicated 20A circuit. Some large window units and through-wall ACs use 240V and need a dedicated 20-30A circuit. Always check the unit's nameplate and ensure it has a dedicated circuit — don't share it with other large appliances.

What size breaker for an electric water heater?

A standard 40-50 gallon electric tank water heater typically draws 18.75A at 240V (4,500W element) and needs a 30A breaker with 10-gauge wire. Because the water heater is a continuous load, the 125% rule applies: 18.75A x 1.25 = 23.4A, which rounds up to a 30A breaker. Tankless electric water heaters draw much more — often 75-150A — and may need multiple dedicated circuits.

Do I need a dedicated circuit for my appliance?

NEC requires dedicated circuits for: refrigerators, dishwashers, garbage disposals, microwaves, washing machines, dryers, water heaters, HVAC equipment, and any hardwired appliance. Kitchen countertop outlets must be on at least two dedicated 20A small-appliance circuits. As a general rule, any appliance that draws more than half the circuit's capacity should have its own dedicated circuit.

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