What size solar system fits your bill?

Size is the capacity that would offset a share of your usage, limited by the roof. It is not a personality and not a national average you must hit.

Start from the bill

Annual usage is roughly your monthly bill divided by your real price, times 12. Our calculator uses the 2025 EIA state average when it does that division, because it does not have your tariff. A $180 bill in a high-price state is fewer kilowatt-hours than the same bill in a low-price state, so the illustrated system is smaller. The dollar range can still match, because both are a share of $180 times 12.

Then the sun and the roof

Peak sun hours and a performance factor turn usage into kilowatts. A sunny El Paso roof needs fewer watts than a cloudier Pittsburgh roof to make the same energy. Shade reduces the share we illustrate and should reduce the installer's model by more than a guess. The roof may not hold the kilowatts the bill suggests. The layout wins.

Berkeley Lab's median 2025 residential system was 7.7 kW, with most systems between about 5 and 12 kW. That describes what was installed. It is not your target.

Bigger is not always better

Extra kilowatts cost money. If the extra energy is exported at a low credit, you may have bought kilowatt-hours the tariff barely pays for. Ask the proposal to split self-consumed energy from exports. Net metering is the reason that split exists. Then run your own bill through the estimate and see whether the proposal is in the same neighborhood before you argue about brand.