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How many solar panels do I need?

Three numbers answer it: how much electricity you use in a year, how much one kilowatt of panels makes where you live, and the watts of the panel you would buy. Your bills give the first, a free government tool the second, the panel's spec sheet the third.

Work out your solar panels

The same rule, without the form
StepHow
Yearly useadd up 12 months of kWh from your bills
System size (kW)yearly kWh / kWh one kW makes where you live
Panelssystem watts / watts of one panel, rounded up
Roof areapanels x 17.5 sq ft (standard) or about 21 sq ft (newer 400+ W)

The 10,791 kWh already typed is the 2022 US average home: replace it with your own. Get the kWh per kW for your address from PVWatts (NREL): divide its yearly kWh by the system size you entered there.

Start from your bills, not from the roof

Each electric bill shows the kilowatt-hours you used that month. Add up the last twelve and you have your yearly use, the number the whole calculation rests on. A year matters because use changes with the seasons: air conditioning in summer, lighting and heating in winter. If you plan an electric car or a heat pump, add their use too, or the system comes out too small.

Why your address changes the answer

The same panel makes much more electricity in a sunny southern state than under cloudy northern skies, and less on a roof that faces away from the sun or sits in the shade of a tree. That is why we do not type a national number for you. The government's free PVWatts tool takes your address, the roof's tilt and direction, and gives the yearly kWh a system would make there, already reduced for normal losses such as dust, wiring and shade.

Panels: watts and size

Fewer, stronger panels cover the same need with less roof. Check the watts and the size on the spec sheet of the exact panel you are offered: the calculator takes both, so the roof area it gives matches your panel, not an average.

Before you ask for quotes

  • Have your twelve months of kWh ready before you ask for quotes.
  • Note which parts of the roof get full sun most of the day.
  • Roof work and wiring to the panel are jobs for licensed professionals, with permits.

Good to know

  • Your electric bill lists the electricity you used in kilowatt-hours (kWh). Add up the last 12 months of bills to get your yearly use.1,2,3
  • In 2022 the average US home used 10,791 kWh of electricity in the year, about 900 kWh a month.4,5
  • How much one kW of panels produces in a year depends on where you live and how much sun the panels get, so the production figure has to match your location.2,5,6
  • NREL's free PVWatts calculator estimates how much electricity a solar system will produce at a location you enter.2,7
  • To get the number of panels, divide the system size by the wattage of one panel; home panels are commonly rated about 250 to 400 watts.2,8,9
  • Newer high-output home panels are rated in the 400s of watts and measure about 68 x 44 inches, roughly 21 square feet each.10,11
  • A standard 60-cell home panel measures about 65 x 39 inches, about 17.5 square feet.8,12
  • Real systems make less than the panels' rated output: PVWatts uses a default total system loss of 14 percent (soiling, shading, wiring and more).2,13
  • In the US, panels facing south work best, and shade from trees or buildings cuts how much they make.2,5,9

How we checked this page

Checked on October 26, 2026. We kept a fact only when two independent publishers agree, and each one is numbered to its sources below. Where sources give different numbers, we keep only what they share. We never write a price. This page was written with an AI assistant and checked against the sources below.

Sources

  1. Planning a Home Solar Electric System, US Department of Energy (Energy Saver)
  2. Working on Solar: Design and System Sizing (FS-2023-0655), University of Maryland Extension
  3. Solar sizing, Eversource
  4. How much electricity does an American home use? (FAQ), US Energy Information Administration (EIA)
  5. How many solar panels do I need?, CNN Underscored
  6. How much energy do solar panels produce? (FAQ), Maxeon Solar Technologies
  7. PVWatts Calculator, National Renewable Energy Laboratory (NREL, US federal)
  8. Solar Panel Size, This Old House
  9. How Many Solar Panels to Power a House, Bob Vila
  10. REC Alpha Pure-R Series datasheet (US), REC Group
  11. Q.TRON BLK M-G2+ series datasheet, Qcells (Hanwha Qcells)
  12. Average solar panel size, Aurora Solar
  13. PVWatts Version 5 Manual, National Renewable Energy Laboratory (NREL, US federal)
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