How Many Solar Panels Do I Need? Size by Usage, State & Roof
The average US home needs 15–25 panels (400W) to cover its bill. Here is how many solar panels you need by monthly kWh usage, state, and coverage goal — with a free sizing calculator.
By The PVFig Editorial Team · 2026-08-10 · reviewed against EIA, NREL and DSIRE sources
The simple formula
Panels = (monthly kWh × 12) ÷ (kWh per kW for your state) ÷ panel watts × 1000. For an average home (875 kWh/month, US average production 1,367 kWh/kW), you need about 8 kW — roughly 20 × 400W panels.
It varies by state
The same 10,500 kWh/year home needs about 13 panels in Arizona (1,755 kWh/kW) but 22 in Massachusetts (1,302 kWh/kW). Sun-rich states need fewer panels; cloudy states need more. Coverage goal matters too — 120–150% if you have an EV or heat pump.
Roof space check
A 400W panel is about 17.5 sq ft. 20 panels need ~350 sq ft of usable south-facing roof plus fire-code setbacks. If your roof is tight, higher-wattage panels (440W TOPCon) reduce the count. Use the PVFig system size calculator for your exact numbers.
FAQ
How many solar panels does the average home need?
About 15–25 × 400W panels (6–10 kW), depending on your usage, state, and sun exposure. The US average home lands near 20 panels / 8 kW.
How many panels for 1,000 kWh per month?
At average US sun you need about 20 × 400W panels (~8 kW). In Arizona you need ~16; in Massachusetts ~24.
How much roof space do solar panels need?
Each 400W panel is roughly 17.5 sq ft. A 20-panel system needs ~350 sq ft of usable south-facing roof.
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Sources
- U.S. EIA — electricity rates by state, eia.gov/electricity/monthly
- NREL PVWatts v8 — solar production by location, pvwatts.nrel.gov
- DSIRE — state incentives and net metering, dsireusa.org
- See how every figure on this page is calculated — PVFig methodology.
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