Solar Panel Calculator: Size, Cost & Payback
Pick your state, enter your monthly electric bill, and see how many panels you need, what they cost, and how long they take to pay for themselves. For a more precise number, open your city's page — it uses local sunshine instead of the state median.
Solar payback calculator
State values are medians across the places we cover. Replace the price per watt with a real installer quote when you have one.
Leave export credit blank where the utility offers full net metering. Where exports earn less, solar used at home as it's produced is worth the full price and the rest earns the export credit.
How many solar panels do I need?
Divide your yearly electricity use (kWh) by how much one kW of panels produces where you live, then divide by the panel size. Example: 10,800 kWh a year ÷ 1,300 kWh per kW = 8.3 kW, or 21 panels of 400 W. Sunny Southwest cities produce 1,600–1,800 kWh per kW; the cloudy Pacific Northwest about 1,100.
What this calculator leaves out
It uses each state's rules for power you send back to the grid — full retail credit under net metering, or a lower export credit where utilities have moved to net billing — and assumes no federal tax credit (it ended for systems installed after 2025) and no battery. See the methodology for every assumption.