How Many Solar Panels Do I Need? A Simple Sizing Guide
Solar installers size systems with the same basic math you can do yourself. Knowing it helps you judge whether a quote is reasonable before you sign anything.
1. Find your yearly electricity use
Add up the kWh from your last 12 electricity bills. If you only have one bill, multiply by 12 — but seasonal changes make the full year more accurate. The average U.S. home uses about 10,400 kWh a year (865 kWh a month, EIA 2024). Add any planned changes, such as an electric car or a heat pump.
2. Look up how much 1 kW of panels produces where you live
Sunshine varies hugely. According to NREL’s PVWatts model, 1 kW of south-facing panels produces about 1,750 kWh a year in Phoenix but only about 1,090 kWh in Seattle; the U.S. average is around 1,370 kWh. Our solar panel calculator includes the figure for every state.
3. Divide to get the system size
System size (kW) = yearly kWh ÷ kWh per kW. For 10,380 kWh in Texas (1,421 kWh per kW): 10,380 ÷ 1,421 = 7.3 kW. With 400 W panels that is 7,300 ÷ 400 = 18.3, so 19 panels.
4. Adjust for your roof
PVWatts figures assume a south-facing roof with a moderate tilt, no shading and about 14% system losses. East- or west-facing roofs typically produce noticeably less, and shading from trees or chimneys can cut output further. Installers model your actual roof; if their production estimate is far above what the math suggests, ask why.
Cost and payback in 2026
EnergySage reports an average installed price of about $2.60 per watt before incentives in 2026, ranging from roughly $2.10 to $3.80 by state. The 30% federal residential solar tax credit ended for systems installed after December 31, 2025, so payback now depends mostly on your electricity rate and any state or utility incentives. The solar cost calculator estimates the price, yearly savings and payback for your state.
For backup during outages, size a home battery with the solar battery calculator.
Frequently asked questions
How many solar panels do I need for 1,000 kWh a month?
At the U.S. average of about 1,370 kWh per kW a year, 12,000 kWh needs about 8.8 kW — 22 panels of 400 W. Sunny states need fewer; cloudy states more.
Is solar still worth it without the federal tax credit?
It depends mainly on your electricity rate and how your utility credits exported power. In high-rate states such as California or Massachusetts, payback can still be well under 10 years.
More guides
- How Much Electricity Does a House Use?How many kWh an average U.S. home uses per month, what drives the bill, and how to find which appliances cost you the most.
- What Size Generator Do I Need for My House?How to size a backup generator: list your essentials, add running watts, cover the largest starting surge and pick a safe size — with examples.
Last updated October 26, 2026