Solar Panel Count Calculator

How to use this calculator

Enter Target capacity (kW), Panel rating (W). The result updates in your browser as you edit an input. The prefilled values are examples only.

How the estimate works

Convert target kW to watts and divide by panel rating; round up to whole panels.

What can change the answer?

Panel count is a capacity estimate, not a roof layout. Fire setbacks, roof obstructions, structural limits, and inverter selection affect a real design.

Before relying on the result

Check that the figures use the same units and period. Compare the result against a current label, quote, contract, employer policy, or official dataset when appropriate. This estimate does not include factors you have not entered.

Further reference

For source data or a more detailed method, see National Laboratory of the Rockies: PVWatts production model. The calculator does not automatically import data from this source.

Worked example with the default inputs

An 8 kW target equals 8,000 watts. Dividing by 400 watts per panel gives 20 panels. A non-integer result is rounded up, but roof fit and electrical design require separate checks.

Interpret the result in a planning record

The panel count calculator converts a target in kilowatts to watts, divides by each panel’s watt rating and rounds up to a whole panel. That tells you a capacity-based count. It does not check roof dimensions, setbacks, obstructions or equipment compatibility. Use the rating of the panel being considered rather than an unrelated example specification.

Save the input values, units and result together. Change one uncertain input at a time so you can see which assumption moves the answer. A displayed decimal is arithmetic precision, rather than evidence that the measurements or rates are equally precise.

More tools

Read the How to Read a Solar Quote Without Mixing Up the Numbers guide →