Breaker Size Calculator | Wire Size & Appliance Ratings
Free online tool • Calculated per NEC 240.6(A), 310.16, 430.52 & 440.22
Use this free breaker size calculator to find the correct circuit breaker rating per NEC 240.6(A). Select your load type — general, motor, HVAC, or welder — and enter the load current or motor horsepower. The calculator recommends the standard breaker size and paired wire gauge.
Recommended Sizing
NEC Standard SizeBreaker Type: Standard Inverse-Time
NEC Reference Note: 125% multiplier applied for continuous loads per NEC 210.20(A).
How to Size a Circuit Breaker
Sizing a circuit overcurrent protection device (breaker) is a vital aspect of electrical safety. The primary purpose of a breaker is to protect the circuit conductors from overheating and causing fires. Standard breaker sizing takes into account the total current drawn by the load and whether that load runs continuously. Under the National Electrical Code, continuous loads (running for 3 hours or more) must be sized at 125% of their rated draw, while non-continuous loads are sized at 100%.
NEC 240.6 Standard Breaker Sizes
NEC Table 240.6(A) defines standard ratings for fuses and inverse-time circuit breakers:
| Category | Standard Amperage Ratings (Amps) |
|---|---|
| Small Branch | 15, 20, 25, 30, 35, 40, 45, 50 |
| Medium Distribution | 60, 70, 80, 90, 100, 110, 125, 150 |
| Large Feeders | 175, 200, 225, 250, 300, 350, 400, 450, 500, 600 |
| Industrial Mains | 700, 800, 1000, 1200, 1600, 2000, 2500, 3000, 4000, 5000, 6000 |
Motor Breaker Sizing (NEC 430.52)
Unlike general branch circuits, electric motors draw significant starting inrush currents. To prevent nuisance tripping on startup, NEC Article 430 allows inverse-time circuit breakers to be sized up to 250% of the motor Full-Load Current (FLC). Note that calculations must reference the standardized FLC tables in NEC Article 430 (such as Table 430.248 for single-phase and Table 430.250 for three-phase motors) rather than nameplate ratings.
| Motor HP (230V 1-Ph) | NEC FLC (Amps) | Max Breaker (250% limit) |
|---|---|---|
| 1/2 HP | 4.9 A | 15 A |
| 2 HP | 12.0 A | 30 A |
| 5 HP | 28.0 A | 70 A |
| 10 HP | 50.0 A | 125 A |
HVAC Breaker Sizing (NEC 440)
Air conditioning and refrigeration equipment have unique compressor motor requirements. In compliance with NEC 440.22, the protection rating for these systems is initially calculated at 175% of the branch-circuit selection current or rated-load current. If this sizing trips during compressor startup, the code permits the overcurrent protection to be upsized to a maximum of 225% to accommodate the inrush.
Appliance Breaker Sizing Guide
Sizing a circuit breaker for specific household and industrial appliances depends on standard code requirements and expected continuous draw. Here are the typical NEC-compliant breaker and wire sizes for common loads:
| Appliance Type | Standard Breaker Size | Required Copper Wire Size |
|---|---|---|
| Electric Water Heater | 30 Amp (240V) | 10 AWG |
| Clothes Dryer | 30 Amp (240V) | 10 AWG |
| Electric Stove / Range / Oven | 40 Amp or 50 Amp (240V) | 8 AWG or 6 AWG |
| Dishwasher & Garbage Disposal | 15 Amp or 20 Amp (120V) | 14 AWG or 12 AWG |
| Mini Split / Air Conditioner (3-ton typical) | 40 Amp (240V) | 8 AWG |
Wire Size to Breaker Sizing Chart
What size wire for a breaker? Paired copper wire sizes are selected from NEC Table 310.16 at 75°C, ensuring small conductor limits are respected for safety:
| Breaker Size (Amps) | Minimum Copper Wire Size (75°C) |
|---|---|
| 15 Amp Breaker | 14 AWG (Copper) |
| 20 Amp Breaker | 12 AWG (Copper) |
| 30 Amp Breaker | 10 AWG (Copper) |
| 40 Amp Breaker | 8 AWG (Copper) |
| 50 Amp Breaker | 6 AWG (Copper) |
| 60 Amp Breaker | 4 AWG (Copper) |
How to Size a Breaker
Determine if load is continuous
Continuous loads run for 3 hours or more (e.g., branch circuit lighting, heaters). Non-continuous loads run for shorter durations.
Calculate load current
Locate or calculate the load draw in Amps. For motors, use FLC tables in NEC Article 430.
Apply NEC multipliers
Multiply by 125% for continuous loads, 175% for HVAC compressor feeds, or 250% for standard motors.
Select breaker rating
Round the calculated ampacity up to the next standard rating listed in NEC Table 240.6(A).
Pair with conductor
Locate the minimum copper conductor gauge whose ampacity matches or exceeds the breaker rating per Table 310.16.
Frequently Asked Questions
What size breaker do I need for a water heater?
A standard residential electric water heater (typically 4,500W at 240V) draws 18.75 Amps. Sized as a continuous load at 125% (23.4 Amps), it requires a standard 30 Amp double-pole breaker paired with 10 AWG copper wire.
What size breaker do I need for a dryer?
A standard household electric clothes dryer requires a dedicated 30 Amp double-pole circuit breaker. This must be wired with 10 AWG copper wire (typically a 10-3 NM-B cable for modern 4-prong receptacles).
What size breaker do I need for an electric stove or range?
Most standard electric kitchen ranges and stoves require a dedicated 40 Amp or 50 Amp breaker, operating at 120/240V. A 40A circuit requires 8 AWG copper wire, while a 50A circuit requires 6 AWG copper wire.
What size breaker do I need for a dishwasher?
A standard household dishwasher requires a dedicated 15 Amp or 20 Amp branch circuit breaker. It is typically wired using 14 AWG copper wire (for a 15A breaker) or 12 AWG copper wire (for a 20A breaker).
Can I use a 30 amp breaker on 12 gauge wire?
No, this is a code violation. Under NEC 240.4(D), the maximum overcurrent protection for 12 AWG copper wire is 20 Amps. A 30 Amp breaker requires a minimum of 10 AWG copper wire to prevent overheating and fire risks.