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.
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
Related Calculators
Always match breaker size to the wire gauge in the circuit. Browse the electrical calculator collection.
FAQ
What counts as a continuous load?
In planning discussions, continuous often means a load expected to run for extended periods. The 125% factor is a common planning adjustment in many contexts.
Does this pick the exact breaker I should buy?
This calculator applies NEC sizing rules and recommends the next standard breaker size up. The result is a strong planning reference, but always verify with a licensed electrician — local codes, panel compatibility, and load type all affect the final breaker selection.
What size breaker do I need for a 240V dryer?
Most residential electric dryers require a 30A double-pole breaker on a dedicated 240V circuit with 10 AWG wire. Heavy-duty or commercial dryers may require 40A. Always check the dryer nameplate for actual amperage — the nameplate rating determines the correct breaker size, not the outlet configuration.
Can I use a 20 amp breaker on 15 amp wiring?
No. The breaker must match the wire gauge — a 20A breaker on 14 AWG wire is a fire hazard because the wire can overheat before the breaker trips. 14 AWG requires a 15A maximum breaker. 12 AWG can use a 15A or 20A breaker. This is one of the most common and dangerous DIY electrical mistakes.
What is the difference between a single-pole and double-pole breaker?
A single-pole breaker controls one hot wire and protects a 120V circuit — used for outlets, lighting, and small appliances. A double-pole breaker controls two hot wires and protects a 240V circuit — used for dryers, ranges, EV chargers, water heaters, and air conditioners. Double-pole breakers take up two slots in the panel. For 240V circuits, breaker ampacity is based on one leg, not the sum.