This is a planning calculator, not a roof-layout tool. The annual-yield input should ideally come from a ZIP-specific PVWatts estimate. Real roof area needs spacing, setbacks, fire-code access paths, obstructions and roof geometry, so the panel footprint is not the same as required usable roof area.
Only have your monthly electric bill?
Use the Solar System Size by Electric Bill calculator to estimate annual kWh first from your state electricity rate and the energy portion of your bill. If your utility account already shows annual kWh, use that actual consumption here instead.
Already know the panel count?
Use the Solar Panel Output Calculator to turn a panel count and wattage into state-level annual, monthly and daily production estimates, or compare standard system output on Solar Production by State.
Use a location-specific solar yield when possible
A generic U.S. yield is useful only for early planning. For a better number, run the Home Solar Calculator with your ZIP code and use the resulting PVWatts production assumption.
Why panel count is not the same as roof fit
- Roof setbacks and fire-code access paths reduce usable area.
- Vents, chimneys, skylights and multiple roof planes affect layout.
- Panel dimensions differ by manufacturer and watt class.
- Shading and orientation can make a smaller roof section more productive than a larger one.
For roof-area planning use the Roof Solar Calculator. For address-level building insights use the Solar Roof Analyzer.