Calculators

How Many Solar Panels Do I Need? Calculator

Calculate how many solar panels you need for your electricity use, the system size in kW and the approximate roof area, based on sun hours in your state.

Updated

Defaults come from our data files (last checked October 24, 2026).

Your estimate

Panels needed

19

System size
7.6 kW
Estimated annual production
10,752 kWh
Approximate roof area
391 sq ft

To produce about 10,366 kWh a year you would need roughly 19 panels of 400 W (7.6 kW), using about 391 sq ft of roof.

This is an estimate, not a quote. Real results depend on your roof, shading, utility tariff, equipment and installer pricing.

How we calculate this

  1. Production per panel per year = panel watts ÷ 1,000 × peak sun hours × 365 × system efficiency. Defaults: a 400 W panel, 5.1 hours of sun per day and 76% system efficiency.
  2. Panels needed = annual use × share to cover ÷ production per panel, rounded up.
  3. System size = panels × panel watts ÷ 1,000.
  4. Roof area = panels × area per panel (default 21 sq ft[src], a 400 W panel at the 20.9% median module efficiency Berkeley Lab reports for 2024 installs).

Next steps

Frequently asked questions

How many solar panels does an average house need?

It depends on how much electricity you use, how much sun you get and the panel wattage. Enter your annual kWh from your utility bill and your state's sun hours to get an estimate for your home.

Will more efficient panels reduce the number I need?

Higher-wattage panels produce more per panel, so you need fewer of them and less roof space. Total system size in kW stays about the same for the same energy goal.

How much roof space do I need?

Multiply the number of panels by the area of one panel. Fire-code setbacks, vents, chimneys and spacing between rows mean you usually need more roof than the panel footprint alone.

Sources

  1. U.S. Distributed Solar and Storage, 2025 Data Update (module efficiency), Lawrence Berkeley National Laboratory (accessed October 24, 2026)
  2. PVWatts Calculator, National Laboratory of the Rockies (formerly NREL) (accessed October 24, 2026)
  3. How much electricity does an American home use?, U.S. Energy Information Administration (accessed October 24, 2026)