Home / System sizing
How Many Solar Panels Do I Need?
Work out how many solar panels and what system size you need, and how much roof they take.
Your result
Enter your numbers and press the button. Your result appears here.
The average U.S. home used 865 kWh a month in 2024, according to the EIA. Use your own bills for a better answer.
How it works
Size (kW) = yearly kWh to cover ÷ yearly kWh per kW. Panels = size in watts ÷ panel watts, rounded up.
Example: 865 kWh a month needs 7.59 kW, or 19 panels of 400 W covering about 399 ft².
At a glance
Same settings as the calculator, changing only the monthly use.
| Monthly use | System | Panels | Roof area |
|---|---|---|---|
| 500 kWh | 4.39 kW | 11 | 231 ft² |
| 750 kWh | 6.58 kW | 17 | 357 ft² |
| 1,000 kWh | 8.78 kW | 22 | 462 ft² |
| 1,250 kWh | 10.97 kW | 28 | 588 ft² |
| 1,500 kWh | 13.17 kW | 33 | 693 ft² |
| 2,000 kWh | 17.56 kW | 44 | 924 ft² |
Solar by state
An 8 kW system at each state's average price per watt, electricity price and output. Payback in years, before incentives.
| State | Per watt | Electricity | kWh per kW | 8 kW cost | Payback |
|---|---|---|---|---|---|
| Alabama | $3.72 | 16.51¢ | 1,367 | $29,760 | 17.2 |
| Alaska | $2.60* | 27.32¢ | 922 | $20,800 | 10.6 |
| Arizona | $2.25 | 15.36¢ | 1,755 | $18,000 | 8.5 |
| Arkansas | $2.37 | 13.74¢ | 1,373 | $18,960 | 12.9 |
| California | $2.52 | 32.58¢ | 1,677 | $20,160 | 4.7 |
| Colorado | $2.63 | 16.80¢ | 1,595 | $21,040 | 10.0 |
| Connecticut | $2.67 | 27.47¢ | 1,291 | $21,360 | 7.7 |
| Delaware | $2.63 | 17.98¢ | 1,364 | $21,040 | 11.0 |
| District of Columbia | $3.20 | 24.86¢ | 1,391 | $25,600 | 9.5 |
| Florida | $2.12 | 15.32¢ | 1,455 | $16,960 | 9.7 |
| Georgia | $2.50 | 15.48¢ | 1,420 | $20,000 | 11.7 |
| Hawaii | $3.44 | 46.41¢ | 1,622 | $27,520 | 4.6 |
| Idaho | $2.95 | 13.02¢ | 1,468 | $23,600 | 16.0 |
| Illinois | $2.92 | 19.23¢ | 1,308 | $23,360 | 11.9 |
| Indiana | $2.59 | 17.04¢ | 1,332 | $20,720 | 11.7 |
| Iowa | $3.26 | 14.55¢ | 1,367 | $26,080 | 17.1 |
| Kansas | $2.66 | 15.26¢ | 1,526 | $21,280 | 11.7 |
| Kentucky | $2.48 | 14.20¢ | 1,343 | $19,840 | 13.4 |
| Louisiana | $2.31 | 13.27¢ | 1,479 | $18,480 | 12.1 |
| Maine | $2.91 | 30.23¢ | 1,319 | $23,280 | 7.4 |
| Maryland | $2.55 | 21.31¢ | 1,392 | $20,400 | 8.8 |
| Massachusetts | $2.90 | 30.19¢ | 1,302 | $23,200 | 7.5 |
| Michigan | $2.86 | 21.73¢ | 1,291 | $22,880 | 10.4 |
| Minnesota | $3.23 | 16.44¢ | 1,333 | $25,840 | 15.3 |
| Mississippi | $2.29 | 15.06¢ | 1,414 | $18,320 | 11.0 |
| Missouri | $2.49 | 14.28¢ | 1,433 | $19,920 | 12.5 |
| Montana | $2.54 | 14.13¢ | 1,344 | $20,320 | 13.8 |
| Nebraska | $2.60* | 12.92¢ | 1,423 | $20,800 | 14.6 |
| Nevada | $2.35 | 13.36¢ | 1,753 | $18,800 | 10.3 |
| New Hampshire | $2.88 | 26.91¢ | 1,258 | $23,040 | 8.7 |
| New Jersey | $2.60 | 24.09¢ | 1,305 | $20,800 | 8.4 |
| New Mexico | $2.49 | 15.34¢ | 1,779 | $19,920 | 9.3 |
| New York | $2.77 | 29.26¢ | 1,291 | $22,160 | 7.5 |
| North Carolina | $2.44 | 14.94¢ | 1,416 | $19,520 | 11.9 |
| North Dakota | $2.60* | 12.46¢ | 1,294 | $20,800 | 16.8 |
| Ohio | $2.56 | 18.81¢ | 1,296 | $20,480 | 10.8 |
| Oklahoma | $2.57 | 13.81¢ | 1,542 | $20,560 | 12.4 |
| Oregon | $2.40 | 15.46¢ | 1,121 | $19,200 | 14.3 |
| Pennsylvania | $2.60 | 21.13¢ | 1,356 | $20,800 | 9.3 |
| Rhode Island | $2.80 | 29.05¢ | 1,294 | $22,400 | 7.6 |
| South Carolina | $2.57 | 15.90¢ | 1,454 | $20,560 | 11.4 |
| South Dakota | $2.60* | 14.58¢ | 1,409 | $20,800 | 13.0 |
| Tennessee | $3.48 | 13.80¢ | 1,338 | $27,840 | 19.7 |
| Texas | $2.26 | 16.03¢ | 1,421 | $18,080 | 10.2 |
| Utah | $2.60* | 13.19¢ | 1,484 | $20,800 | 13.7 |
| Vermont | $2.78 | 23.93¢ | 1,222 | $22,240 | 9.7 |
| Virginia | $2.56 | 16.95¢ | 1,427 | $20,480 | 10.8 |
| Washington | $2.47 | 14.42¢ | 1,088 | $19,760 | 16.4 |
| West Virginia | $2.60* | 15.58¢ | 1,219 | $20,800 | 14.1 |
| Wisconsin | $3.03 | 19.05¢ | 1,334 | $24,240 | 12.3 |
| Wyoming | $2.60* | 14.01¢ | 1,533 | $20,800 | 12.5 |
* No EnergySage state average published; national $2.60 per watt used.
All system sizing calculators
Common questions
How many solar panels does an average house need?
The average U.S. home used 865 kWh a month in 2024. At the national average output of 1,367 kWh per kW, that takes about 7.6 kW, or 19 panels of 400 W.
How much roof space do solar panels need?
A 400 W panel is about 21 ft², so 20 panels cover about 420 ft² before walkways and setbacks.
Should I cover 100% of my use?
Under full net metering, yes. Where exports earn less, a smaller system that matches your daytime use may pay back faster.
Sources
- U.S. EIA, Today in Energy: average residential use 865 kWh a month in 2024: https://www.eia.gov/todayinenergy/detail.php?id=65244
- NREL PVWatts v8 (20° tilt, south-facing, 14% losses), state results compiled by TheGreenWatt: https://thegreenwatt.com/average-peak-sun-hours-by-state/
- EnergySage, Solar panel cost by state (updated November 6, 2026): https://www.energysage.com/local-data/solar-panel-cost/
- U.S. EIA, Electric Power Monthly, Table 5.6.B (residential price, Jan–Aug 2026): https://www.eia.gov/electricity/monthly/epm_table_grapher.php?t=epmt_5_6_b