Electrical Load Calculator

How this electrical load calculator works

This calculator estimates your home's total electrical demand and compares it to your panel's capacity, so you can see whether you have room to add a new load, like an EV charger, a Tesla Powerwall, or a heat pump, before scheduling work.

It follows the same logic a licensed electrician uses in a standardized load calculation: it sums your home's general lighting and receptacle load, fixed appliances, and the largest motor loads, then checks the total against your service rating (commonly 100, 150, or 200 amps).

Why a load calculation matters

Adding a large 240-volt load to a panel that's already near capacity can trip breakers, overheat connections, and create a genuine fire risk. A load calculation is how you confirm, with numbers, not guesswork, that your service can safely handle what you want to add.

It can also save you thousands. Many homeowners assume they need a panel upgrade before adding an EV charger, when in fact they have spare capacity or can use smart load management instead. The calculation tells you which camp you're in.

What affects your available capacity

• Your service size, 100A leaves far less headroom than 200A
• Existing large loads: central A/C, electric range, dryer, water heater
• Whether your heating is electric (heat pump, baseboard) or gas
• The amperage of the new load you want to add
• Whether load management can stagger high-draw devices

From estimate to a real answer

Treat this tool as a planning aid, not a permit. A real load calculation accounts for code-required demand factors and the specifics of your panel. If your estimate lands anywhere close to your service limit, the next step is a free in-home assessment, where an electrician verifies the numbers and inspects your panel and service entrance.

If the result shows you're tight on capacity, see how much a panel upgrade costs and the panel upgrade rebates that can offset it.

Reading your result like an electrician

The number that matters is your margin, not just pass/fail. Computed demand under 70% of service rating: comfortable headroom, add the charger or battery without ceremony. Between 70% and 90%: workable, but plan additions deliberately and consider load management for the big ones. Above 90%: you're living at the edge, and the next major appliance decision doubles as a service-size decision.

Remember what the calculation can't see: the physical panel's condition and breaker space, local code amendments, and the difference between computed demand (code math) and your actual peaks (usually lower). That's why the free assessment pairs this math with eyes on the equipment, the two together produce the real answer.

Worked example: the 100-amp question

A 1,800 sq ft home, gas furnace and water heater, central air, electric dryer and range. General load: 1,800 × 3W + 3,000W small appliance/laundry = 8,400W, with demand factors ≈ 4,890W. Add A/C (4,000W), range (8,000W demand-factored), dryer (5,000W): total ≈ 21,900W ÷ 240V ≈ 91A computed. On 100A service that's tight-but-legal; adding a 40A EV charger pushes past, enter load management (charge at night when the range sleeps) or the 200A conversation.

Run your own numbers above, then notice which single load moves your result most. For most homes it's electric heat or the range, and that observation often reshapes electrification plans more usefully than any rule of thumb.