Electrical Panel Load Calculator

Every home has a main electrical panel that limits total power draw. Panels are rated in amps — common sizes are 100A, 150A, 200A, and 400A for larger homes. The product of amps and voltage (240V for U.S. residential service) gives total capacity in watts.

200A x 240V = 48,000 W = 48 kW maximum capacity.

The 80% continuous rule

NEC Section 220.87 and general practice limits continuous loads to 80% of panel capacity. Continuous means running for 3 or more hours at a time — HVAC, lighting circuits, and EV chargers are continuous loads. Intermittent loads like ovens, microwaves, and power tools can use the full 100%.

For planning additions (an EV charger, a hot tub, an addition), the conservative approach is to keep total load under 80% of panel capacity. If adding a 50A EV circuit would push you over 80%, a service upgrade may be needed.

Calculating total load

Add up the amperage of all installed breakers. But this overstates actual load — you cannot draw maximum from every circuit simultaneously. The NEC load calculation method (Article 220) applies demand factors: the first 10 kVA of general lighting is counted at 100%, the remainder at 35%. Large appliances are counted at defined percentages.

This calculator uses a simplified approach: total connected load versus panel rating. For a formal load calculation for permits or service upgrades, consult a licensed electrician.

A 200A panel with 160A of breakers installed is common and fine — breaker space is not the same as load. What matters is simultaneous draw.