Circuit Load Calculator
Estimate a practical circuit load limit or recommended breaker size for common single-phase and three-phase systems.
This is a circuit-level planning tool for 120V, 240V, 208V 3-phase, and 277/480V 3-phase systems.
Enter the circuit details to estimate a practical load limit.
Estimated result
Max safe amps
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Max safe watts
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Recommended breaker
Using entered breaker
Status
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Run the calculator to see a practical amperage, wattage, and breaker estimate for the selected system.
What does the 80% rule mean?
Breakers are not meant to run at full capacity continuously.
That is why long-running loads are commonly planned around 80% of breaker rating, or sized at 125% from the load side.
Three-phase systems deliver power differently than single-phase systems, so the calculator uses the standard three-phase power relationship internally for those options.
This calculator is a practical planning reference only. It is not a full panel, feeder, or service demand calculator. Final sizing depends on conductor type, equipment, installation details, demand factors, and applicable code requirements.
Related problems and reference
Planning and safety note
This content is for general learning and planning. Always verify work against current NEC requirements, manufacturer instructions, and local code rules. If you are unsure or see heat, sparks, burning smell, repeated trips, or damaged wiring, contact a licensed electrician.