Electrical Panel Load Calculator
Estimate the total ampere demand on an electrical panel by applying NEC-style load factors to lighting, receptacle, appliance, and motor circuits, then check it against the panel's main breaker rating. Ideal for panel schedule design, load additions, and service upgrade evaluations.
Last updated: September 2026
Formula below · 2 sources (ieee.org, Wikipedia) · Updated Sep 2026
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About this calculator
NEC load calculations apply different factors to different load types. This calculator uses: lighting at 100%; receptacle loads at 100% for the first 10,000 VA and 50% above that (NEC 220.44, non-dwelling receptacles); appliance loads at 100% (NEC 220.53 permits 75% only for four or more fastened-in-place appliances in a dwelling, so 100% is the conservative choice); and motor loads at 125% (NEC 430.24 adds 25% of the largest motor; applying it to all motor load is conservative). Panel Current (A) = (lighting + receptacles after 220.44 + appliances + motors × 1.25) / voltage. The result is not capped, so a value above the main breaker rating shows how far the panel is overloaded. For a 480 V three-phase panel, dividing by 480 (rather than √3 × 480) overstates the per-phase current, which errs on the safe side. Continuous loads also need 125% on the feeder (NEC 215.2); have a licensed electrician do the full NEC Article 220 calculation.
How to use
Assume a 120/240 V panel (voltage = 240 V) rated at 200 A, with lightingLoad = 3,000 W, receptacleLoad = 8,000 W, applianceLoad = 6,000 W, and motorLoad = 2,000 W. Step 1 — receptacles: 8,000 W is under 10,000 VA, so it counts at 100%. Step 2 — weighted load: 3,000 + 8,000 + 6,000 + (2,000 × 1.25) = 19,500 W. Step 3 — convert to amps: 19,500 / 240 = 81.25 A, about 41% of the 200 A rating. The defaults (3,000 + 4,500 + 12,000 + 7,500 × 1.25 W) give 28,875 / 240 = 120.3 A.
Frequently asked questions
Why is motor load multiplied by 1.25 in panel load calculations?
The NEC (Article 430) requires that branch circuits feeding motors be sized at 125% of the motor's full-load current to handle continuous running and the increased current drawn during normal operation. Motors can also draw 6–8× their rated current during starting, and while that transient is short, the wiring and breaker must not trip under normal starts. Using a 1.25 multiplier in the panel load calculation ensures the service and panel are adequately sized for all motor-connected loads without nuisance tripping.
What happens if my calculated panel load exceeds the main breaker rating?
If the calculated demand current exceeds the main breaker rating, the panel is overloaded and the main breaker will trip under peak conditions—or worse, the wiring could overheat if the breaker is faulty. In this situation you must either reduce the connected load, add a sub-panel fed from a larger service, or upgrade the service entrance to a higher amperage. A licensed electrician or engineer should perform a full NEC Article 220 service load calculation before any upgrade.
How does panel voltage affect the ampere load calculation for a residential service?
Higher voltage means less current for the same amount of power, following P = V × I. A 240 V panel draws half the current of a 120 V panel for the same watt load, which is why large appliances like dryers and ranges are wired at 240 V—it keeps conductor and breaker sizes manageable. When you enter the correct panel voltage, the calculator converts total watts to amps accurately. Entering the wrong voltage will either under- or over-state the ampere demand, potentially leading to an incorrectly sized service.