How Many Solar Panels Do I Need?
Enter your yearly electricity use from your bill, how much of it you want solar to cover and the panel wattage, and get the system size, the number of panels and the roof area for your state.
Solar panels needed
D02Scenario A
Sets the electricity rate. Pick US average if you're not sure.
From EIA for US average. Use the rate on your bill if you know it.
Rate used: 18.4¢/kWh · US average · EIA reference 2025–26 · 1,350 kWh per kW of solar (data as of 2026-09-26) ·
Panels needed
A 8.0 kW system covers 100% of 10,800 kWh a year in US average.
- System size needed (kW)
- 8.0
- Panels
- 20
- Roof area (~18 sq ft per panel)
- 360 sq ft
- Production per kW in US average
- 1350 kWh a year
Estimate. Formula and sources are under “How it works”. Change any input; the result updates as you type.
2026 note: The federal 25C and 25D tax credits ended for installations after Dec 31, 2025. Our numbers use 2026 rules. State rebates, HEAR/HOMES programs and utility programs may still apply.
Formula
How it works
- System size (kW) = yearly kWh × share to cover ÷ your state's yearly kWh per kW
- Panels = kW × 1,000 ÷ panel watts, rounded up to a whole panel
- Roof area = panels (before rounding) × 18 sq ft
The state's production per kW assumes panels facing south, tilted at the latitude, with 14% system losses. A west-facing or flatter roof produces less, so it needs more panels; the Solar Panel Output calculator shows how much less.
Sources: production per kW per year by state from NREL PVWatts v8 (tilt = latitude, south, 14% losses); US average use of 10,800 kWh per year from the EIA; 2026 panels of 400–450 W at about 18 sq ft each.
Worked example
A worked example
Arizona panels produce about 1700 kWh per kW per year. To cover 14,000 kWh you need 14,000 ÷ 1,700 = 8.2 kW of panels. At 450 W each that's 19 panels, taking about 329 sq ft of roof.
Reference
By state, at the default inputs
Panels needed, with this page's default inputs and each state's reference prices (EIA reference 2025–26, data as of 2026-09-26).
| US average | 20 × 420 W | 18.4¢/kWh |
|---|---|---|
| Alabama | 20 × 420 W | 15.5¢/kWh |
| Alaska | 29 × 420 W | 25.0¢/kWh |
| Arizona | 16 × 420 W | 15.0¢/kWh |
| Arkansas | 20 × 420 W | 13.0¢/kWh |
| California | 17 × 420 W | 32.0¢/kWh |
| Colorado | 17 × 420 W | 16.0¢/kWh |
| Connecticut | 22 × 420 W | 30.0¢/kWh |
| Delaware | 21 × 420 W | 17.0¢/kWh |
| District of Columbia | 21 × 420 W | 19.0¢/kWh |
| Florida | 19 × 420 W | 15.0¢/kWh |
| Georgia | 20 × 420 W | 14.5¢/kWh |
| Hawaii | 18 × 420 W | 42.0¢/kWh |
| Idaho | 19 × 420 W | 12.0¢/kWh |
| Illinois | 21 × 420 W | 17.0¢/kWh |
| Indiana | 22 × 420 W | 15.5¢/kWh |
| Iowa | 21 × 420 W | 13.5¢/kWh |
| Kansas | 18 × 420 W | 14.5¢/kWh |
| Kentucky | 22 × 420 W | 13.0¢/kWh |
| Louisiana | 20 × 420 W | 12.5¢/kWh |
| Maine | 22 × 420 W | 26.0¢/kWh |
| Maryland | 21 × 420 W | 19.0¢/kWh |
| Massachusetts | 21 × 420 W | 29.0¢/kWh |
| Michigan | 23 × 420 W | 19.5¢/kWh |
| Minnesota | 21 × 420 W | 15.5¢/kWh |
| Mississippi | 20 × 420 W | 13.5¢/kWh |
| Missouri | 20 × 420 W | 13.0¢/kWh |
| Montana | 20 × 420 W | 13.0¢/kWh |
| Nebraska | 19 × 420 W | 12.0¢/kWh |
| Nevada | 16 × 420 W | 15.0¢/kWh |
| New Hampshire | 22 × 420 W | 27.0¢/kWh |
| New Jersey | 21 × 420 W | 22.0¢/kWh |
| New Mexico | 16 × 420 W | 15.0¢/kWh |
| New York | 22 × 420 W | 25.0¢/kWh |
| North Carolina | 20 × 420 W | 14.5¢/kWh |
| North Dakota | 20 × 420 W | 11.5¢/kWh |
| Ohio | 23 × 420 W | 16.5¢/kWh |
| Oklahoma | 18 × 420 W | 13.0¢/kWh |
| Oregon | 23 × 420 W | 14.5¢/kWh |
| Pennsylvania | 22 × 420 W | 18.5¢/kWh |
| Rhode Island | 21 × 420 W | 29.0¢/kWh |
| South Carolina | 20 × 420 W | 15.0¢/kWh |
| South Dakota | 20 × 420 W | 13.0¢/kWh |
| Tennessee | 20 × 420 W | 13.5¢/kWh |
| Texas | 18 × 420 W | 15.5¢/kWh |
| Utah | 18 × 420 W | 12.0¢/kWh |
| Vermont | 22 × 420 W | 22.0¢/kWh |
| Virginia | 20 × 420 W | 15.5¢/kWh |
| Washington | 25 × 420 W | 12.0¢/kWh |
| West Virginia | 23 × 420 W | 15.5¢/kWh |
| Wisconsin | 22 × 420 W | 17.5¢/kWh |
| Wyoming | 18 × 420 W | 12.5¢/kWh |
Questions
FAQ
How many solar panels for a 2,000 sq ft house?
Size by electricity use, not by floor area: two houses of the same size can use very different amounts. At the US average of 10,800 kWh a year and 1,350 kWh per kW, you need about 8.0 kW, or 20 panels of 420 W on about 343 sq ft of roof. In Texas (1,450 kWh per kW) the same use needs 7.4 kW and 18 panels.
Does roof direction matter?
Yes. In PVWatts averages, a west-facing roof produces about 87% of a south-facing one, an east-facing roof 86% and a north-facing roof 65%. Divide the system size by that share to keep the same yearly output.
What if my roof is too small?
Lower the share to cover. At 0.9 in Massachusetts, 7,000 kWh a year needs 5.0 kW, or 13 panels of 400 W on about 227 sq ft. Higher-wattage panels also cut the count: the same roof fits more kW.
Should I size for more than my current use?
If you plan to add an EV, a heat pump or an electric water heater, raise the share above 1.0. Check how much those add with the EV charging and heat pump calculators first.
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