Solar System Size Calculator
Find the right solar system size in kW and number of panels for your home, based on your electricity usage, state, and coverage goal.
How this calculator works
- Find the right solar system size for your home: enter your monthly kWh usage, pick your state (sets solar production), and set your bill coverage goal.
- The calculator returns system size in kW, number of 400W panels, roof area needed, and gross cost estimate.
- Use 120–150% coverage if you have an EV or plan to electrify — your future usage matters as much as today's.
Disclaimer: All figures are estimates based on public 2026 data (EIA, NREL PVWatts, DSIRE) and your inputs — not a quote, tax advice, or financial advice. The federal residential solar credit (Section 25D) expired December 31, 2025. Verify with your utility, a licensed installer, and a tax professional before signing anything.
Example scenarios
Average home (875 kWh): ~8 kW, 20 panels at average US sun.
High usage + EV (1,200 kWh): ~11 kW, 27 panels, 120% coverage.
Data & algorithm
- System kW = (monthly kWh × 12 × coverage) ÷ state kWh-per-kW.
- Panels = system kW × 1000 ÷ 400. Roof area = panels × 17.5 sq ft.
- Gross cost = system kW × 1000 × state $/W.
Official data sources
- NREL PVWatts v8 (production), LBNL (cost), EIA RECS (average usage).
All figures dated 2026. Incentives and rates change — verify current values with your utility and the administering authority before making decisions.
Frequently asked questions
How many solar panels do I need for my house?
The average US home (875 kWh/month) needs about 20 × 400W panels (~8 kW). Sun-rich states need fewer; cloudy states more.
Should I oversize my solar system?
If you plan an EV or heat pump, yes — 120–150% coverage avoids re-contracting later. In net-billing states, don't oversize beyond what you can self-consume.