Breaker Size Calculator
Estimate a standard breaker size from load current with optional continuous-load adjustment.
Your Breaker Estimate
- Enter amps - Use the expected current draw in amps.
- Pick load type - Continuous loads often use a 125% planning adjustment.
- Calculate - The tool selects the next standard breaker size at or above the adjusted amps.
- Compare utilization - Utilization helps you see how close the breaker is to the adjusted load.
- Use wire sizing too - Breaker sizing and wire sizing work together, not independently.
Breakers protect the wire, so they come in fixed standard sizes - 15, 20, 30, 40, 50, 60 amps and up (NEC 240.6). For a continuous load, one that runs three hours or more, size the breaker at 125 percent of the load and round up: a 40 amp continuous load needs a 50 amp breaker, while a 40 amp non-continuous load takes a 40. One catch from the wire side: 14, 12, and 10 AWG copper are capped at 15, 20, and 30 amp breakers no matter what, so the conductor can hold the breaker below what the load math alone suggests. Enter your load amps above.
Load to Breaker in Two Steps
How Breaker Size Is Planned
A breaker is typically chosen to protect the wiring and equipment while allowing normal operating current. This calculator uses your load estimate and common breaker steps to suggest a planning-size breaker.
Some loads are treated as “continuous” in planning (expected to run for long periods), which can push the breaker size up to the next standard rating. Always confirm with local code rules and the equipment nameplate before installing anything.
Example: if your calculated load is close to a standard breaker rating, choosing the next size up may be appropriate when continuous duty or inrush is involved. Pair this with the Wire Size Calculator to make sure the conductor can support the selected breaker.
Standard Breaker Sizes (Common)
| Small Sizes | Mid Sizes | Larger Sizes |
|---|---|---|
| 15, 20, 25 | 30, 35, 40 | 50, 60, 70 |
| 80, 90 | 100, 110, 125 | 150, 175, 200 |
This list is used by the calculator to select a “next standard size.”
Method Used
This tool applies:
Breaker = Choose next standard breaker size ≥ A_adj
Code Notes & Sources
- Overcurrent devices are made in fixed standard ampere ratings - 15, 20, 25, 30, 35, 40, 45, 50, 60 and up - so the calculator rounds your load up to the next one on the list.NFPA 70 (NEC) 240.6(A) - Standard Ampere Ratings
- A continuous load must be served by an overcurrent device rated at least 125 percent of that load, which is why the continuous option raises the size. Non-continuous loads use the load current directly.NFPA 70 (NEC) 210.20(A) - Continuous Loads
- Even when the load math allows a larger breaker, 14, 12, and 10 AWG copper are limited to 15, 20, and 30 amp overcurrent protection, so the conductor can cap the breaker. Check the wire size alongside this result.NFPA 70 (NEC) 240.4(D) - Small Conductors
Next Steps
A breaker is only right if the wire and load agree. Confirm both:
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