Size.Solar

    Solar production calculator

    Solar panel wattage & system size calculator

    Enter the monthly kWh from your electricity bill, choose a city, and add the wattage from a panel quote. See the array size and panel count needed for your usage, then compare the quote with estimated annual production and usable roof space.

    Required array size

    Turn monthly usage into a practical DC system target.

    Panels needed

    Compare module counts across common panel wattages.

    Full project

    Carry the estimate into roof, battery, and supplier decisions.

    Solar panel wattage estimate

    Choose a city to load a PVWatts-backed production estimate.

    Use the monthly kWh shown on your electricity bill.

    Enter the rated watts from the panel datasheet or quote.

    Compare this entered array with the recommended panel count.

    Choose a city first

    Then this card will show per-panel output, array production, bill value, and the panel count needed for your usage.

    What solar panel wattage do you need?

    Your electricity use and local solar resource determine the total array size. The watt rating on each panel determines how many modules are needed to reach that target. A higher-watt panel can reduce the panel count, but it does not reduce the amount of energy your home uses.

    1. Read your bill

    Enter average monthly electricity use in kWh, not the bill amount in currency.

    2. Add the panel rating

    Use the rated watts printed on a proposed panel's datasheet, whether it is 400 W, 450 W, 600 W, or another value.

    3. Compare the result

    Check recommended DC system size, panels needed, annual output, and whether the entered quote covers your usage.

    Planning formula: required panel count equals the energy-matched array watts divided by watts per panel, rounded up to a whole module. Final equipment selection must also satisfy usable roof area, shade, electrical string limits, inverter compatibility, wind loading, and local connection rules.

    Browse supported city calculators

    Choose a city for a detailed PVWatts production breakdown, or use the quick estimator above to carry panel count and monthly usage into a roof project.

    Africa

    17 locations

    Asia

    17 locations

    Australia

    5 locations

    Europe

    19 locations

    North America

    17 locations

    South America

    9 locations

    Solar data assumptions

    The quick estimator requests PVWatts® Calculator data from NLR for the selected city in the browser. Detailed city pages use a clearly labelled, latitude-based planning model so they remain fast and available. Build a project to check the estimate against provider-backed weather, your roof, and shade.