Solar Panel Calculator
Find out how many solar panels your home needs. Choose your state, enter your monthly electricity use and panel size, and get the number of panels and the system size.
- System size
- 7.6 kW
- Yearly production
- about 10,800 kWh
- Yearly usage covered
- 10,380 kWh
- Production per kW in Texas
- 1,421 kWh a year
What you will need
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How this calculator works
Yearly need = monthly kWh × 12 × the share you want to cover. System size in kW = yearly need ÷ the yearly production of 1 kW of panels in your state. Panels = system size ÷ panel wattage, rounded up.
Production per kW comes from NREL’s PVWatts v8 model for each state’s largest city, assuming a south-facing roof at 20° tilt and PVWatts’ default 14% system losses, as compiled by TheGreenWatt. For your exact address, run PVWatts yourself.
East- or west-facing roofs, shading and steep or flat roofs produce less, so you may need more panels than this estimate.
Example: 865 kWh a month in Texas with 400 W panels
- Yearly need: 865 × 12 = 10,380 kWh.
- System size: 10,380 ÷ 1,421 kWh per kW = 7.3 kW.
- Panels: 7,305 W ÷ 400 W = 18.3, so 19 panels (7.6 kW).
Quick reference
| State | kWh per kW per year |
|---|---|
| New Mexico | 1,779 |
| Arizona | 1,755 |
| California | 1,677 |
| Texas | 1,421 |
| New York | 1,291 |
| Washington | 1,088 |
| U.S. average | 1,367 |
Tips before you buy
- Size for the next few years: an EV or a heat pump can add thousands of kWh a year.
- Check how your utility credits solar power you export (net metering) — it changes the best system size.
- Use the solar cost calculator to estimate the price and payback for this system.
Common sizes
- Alabama
- Alaska
- Arizona
- Arkansas
- California
- Colorado
- Connecticut
- Delaware
- District of Columbia
- Florida
- Georgia
- Hawaii
- Idaho
- Illinois
- Indiana
- Iowa
- Kansas
- Kentucky
- Louisiana
- Maine
- Maryland
- Massachusetts
- Michigan
- Minnesota
- Mississippi
- Missouri
- Montana
- Nebraska
- Nevada
- New Hampshire
- New Jersey
- New Mexico
- New York
- North Carolina
- North Dakota
- Ohio
- Oklahoma
- Oregon
- Pennsylvania
- Rhode Island
- South Carolina
- South Dakota
- Tennessee
- Texas
- Utah
- Vermont
- Virginia
- Washington
- West Virginia
- Wisconsin
- Wyoming
Guides
Frequently asked questions
How many solar panels does it take to power a house?
An average U.S. home using 865 kWh a month needs roughly 15 to 25 panels of 400 W, depending on how sunny the state is.
How much electricity does one solar panel produce?
In the contiguous U.S., a 400 W panel produces about 440 to 710 kWh a year depending on location, or roughly 1.2 to 2 kWh a day.
Related calculators
- Solar Cost & Payback CalculatorEstimate the cost and payback of rooftop solar.
- Solar Battery Size CalculatorSize a home battery for backup or solar storage.
- Electric Bill CalculatorEstimate your monthly electric bill.
- EV Charging Cost CalculatorFind out what charging an electric car at home really costs.
Last updated October 26, 2026