Solar PV Sizing Calculator: How Many Panels Do I Need?
Estimate the solar array size and approximate panel count needed to match a chosen amount of electricity consumption.
Solar Panel Sizing Calculator
PV sizing is an energy-balance estimate, not a roof design
A preliminary PV size starts with electricity consumption and expected solar resource, then adjusts for system losses. Final array size can also be limited by usable roof area, shading, orientation, module dimensions, local interconnection rules and future electrification loads such as EV charging or heat pumps.
After sizing, estimate installed cost with the Solar Installation Cost Calculator and review Solar Panel Installation Cost.
This is a first-pass estimate. Roof orientation, shading, module temperature, inverter clipping, local weather and export rules can materially change the final design.
Frequently asked questions
Can I size solar from my electric bill?
Yes. Annual kWh from your utility bills is a good starting point for a preliminary system size.
Why are peak sun hours important?
They translate local solar resource into an equivalent number of full-power hours per day.
Estimates only. Actual energy use and costs vary by equipment, climate, tariffs, installation conditions and user behavior.
Location-specific solar data: Use the live location-based PVGIS calculator to calculate with PVGIS irradiation and PV yield for a selected city or coordinates.
WATTCOSTLAB / COST PLANNING
How many solar panels do I need? Use a sizing formula
A first-pass PV size estimate starts with annual electricity use and local solar resource. Convert the energy target into required system capacity using peak sun hours and a system-loss assumption, then divide the required watts by the selected panel wattage to estimate panel count.
Why solar panel count changes by location
The same household electricity use can require a different PV capacity in different climates because solar resource, roof orientation, shading, temperature and system losses vary. Use location-specific solar data before treating a panel count as final.
Related calculators and guides
Quick questions
How do I calculate how many solar panels I need?
Estimate required PV capacity from annual electricity use, local solar resource and system losses, then divide system watts by the wattage of one panel.
Why can two homes with the same annual kWh need different panel counts?
Location, roof orientation, shading, panel efficiency and system losses change the energy produced by each installed kilowatt of PV.