Solar Panel Calculator
Find out how many panels cover your electric bill, how big the system is and how much roof it takes.
Type in what you use, or what you pay, and this calculator tells you how many panels it takes to cover it. It uses sun data for your ZIP code, so a home in Phoenix and a home in Seattle get different answers.
Start with the kWh figure on your bill. If you only know the dollar amount, switch to bill mode and the tool divides it by your state’s price per kWh. Aim for 100% of your use unless your utility pays little for extra power.
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Planning estimates only. Your roof, equipment, utility rules and weather change the real numbers, so get a written quote before you buy. Data as of October 2026.
How this calculator works
The tool works out your yearly use, then divides it by the energy one kW of panels makes in your area. That gives the system size, which is then rounded up to whole panels of the wattage you picked.
The yield per kW comes from a model of the sun on a tilted panel, month by month. It includes panel heat and the 14% loss that NREL’s PVWatts calculator uses by default for dirt, wiring, shade and downtime. We checked the model against PVWatts at eight places across the country, and it matched within about 6%.
Roof area comes from your panel’s efficiency. A 400 W panel at 21% efficiency covers about 20 square feet.
What it leaves out
- Shade. If trees or a chimney shade the roof, raise the loss figure or add panels.
- Usable roof. Fire-code setbacks and vents take space at the edges. Your installer will confirm the layout.
- Future use. An electric car driven 12,000 miles uses roughly 3,500 kWh a year. If one is coming, add it now.
Where the numbers come from
- EIA, How much electricity does an American home use? About 899 kWh a month in 2022.
- NREL PVWatts Calculator, used to check the model and for the 14% default loss.
Questions
How many solar panels do I need to run my house?
It depends on how much power you use and how much sun you get. Enter your kWh and ZIP code above and the tool gives you the count. A home in a sunny state needs fewer panels than the same home in a cloudy one.
How many kWh does the average home use?
The EIA reports 10,791 kWh a year for the average US home in 2022, or about 899 kWh a month. Your bill shows your own figure, and that’s the one to use.
Should I cover 100% of my bill?
Usually yes, if your utility credits extra power at or near the price you pay. If it pays much less for exports, covering 70 to 90% of your use can make more sense. Ask your utility how net metering works.
Does panel wattage change how many panels I need?
Yes. The system size in kW stays about the same, but higher-watt panels mean fewer of them. Most new home panels are 380 to 450 W.
Why does the tool ask for roof tilt and direction?
Both change how much sun the panels catch. A south-facing roof makes the most in the US. East and west roofs make less, and north-facing roofs much less.
Does this include a battery?
No. A battery doesn’t change how many panels you need to cover your yearly use. Use the Solar Battery Calculator to size one.
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