How many solar panels do I need? (the 2026 math)

"How many panels do I need?" has an honest answer: it depends on your usage, your roof's sun, and the panel you pick — and nobody can give you a number before the first two are known. This guide shows the three-step math, with a worked example.

Step 1 — annual usage (from your bill)

Take a full year of bills (or 12 × an average month) and divide by your rate to get annual kWh. The national average home uses roughly 10,500 kWh a year (EIA), but your own number is what matters — a family with an EV and electric heat can easily double it.

Step 2 — system size (the ~1,200 rule)

In the U.S. sun belt, ~1,200 kWh per year per installed kW is the standard planning figure; colder or cloudier states land lower, sunnier ones higher. Divide your annual usage by 1,200 to estimate system size in kW DC. Example: 10,500 kWh ÷ 1,200 ≈ 8.8 kW.

Step 3 — panel count (divide by the module)

Divide the kW by the module rating in kW. With a typical 400 W (0.4 kW) panel: 8.8 ÷ 0.4 = 22 panels. At 430 W you'd need 21; at 350 W, 26. The panel's physical size mostly does not change the count math — its wattage does.

Roof reality check: these three steps ignore orientation, shade and roof area. A south-facing unshaded roof is the ideal; east/west splits and trees push the size up. Your installer's shade analysis is what converts the math into a layout — ask for it before signing anything.

Run your own numbers in the payback estimator — it shows the panel count as it sizes the system to your bill.

Sources

U.S. EIA — average annual electricity consumption for a residential customer — accessed 2026-08-08.
~1,200 kWh/kW planning figure: industry-standard sizing rule used by the U.S. DOE Solar Energy Technologies Office guidance; treat as regional estimate, not a guarantee.