Choosing the Right Solar System Size for Your Home
Too small and you still pay the utility; too big and you overpay. Here is how to size a solar system to your bill, future usage, and state — with the numbers.
By The PVFig Editorial Team · 2026-08-10 · reviewed against EIA, NREL and DSIRE sources
The sizing formula
System kW = (monthly kWh × 12 × coverage goal) ÷ your state's kWh-per-kW. For an average home (875 kWh/month) at average US production (1,367 kWh/kW), that is about 7.7 kW — roughly 19–20 × 400W panels.
Account for the future
If you plan an EV or heat pump, size for 120–150% coverage now — adding panels later is expensive and may hit interconnection caps. In net-billing states, don't oversize beyond what you can self-consume, or exports earn little.
Use your state's real production
Production per kW ranges from ~1,088 kWh (Washington) to ~1,755 kWh (Arizona). The same home needs ~6.2 kW in Arizona but ~9.7 kW in Washington. The PVFig system size calculator uses your state's number automatically.
FAQ
What size solar system does an average home need?
About 7–8 kW (roughly 19–20 × 400W panels) for a home using 875 kWh/month at average US sun.
Should I oversize my solar system?
Oversize to 120–150% if you plan an EV or heat pump. In net-billing states, match sizing to your self-consumption instead.
Can a solar system be too big?
Yes — in net-billing states exports pay little, so a too-big system has a worse payback. Sizing calculators that ignore net metering overstate the benefit.
Ready to compare real installer quotes?
The estimates above are based on public data — your actual price depends on your roof, installer, and market. EnergySage collects quotes from pre-screened installers in one place (free, no obligation).
Compare quotes on EnergySage →
We may earn a commission if you sign up through links above — it never affects our data or estimates.
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.
Comments powered by GitHub Discussions — enable by configuring the Giscus repo in
app/components/Comments.tsx.