The formula for how many solar panels you need
You need enough panels to produce your yearly use, and three numbers decide it: how much electricity you use, how much one kilowatt of panels makes where you live, and the wattage of each panel.
- Yearly use: add up 12 months of bills, or multiply a monthly average by 12. 863 kWh a month is 10,356 kWh a year.
- System size: divide by the local output of 1 kW. Near Denver, PVWatts models 1,595 kWh a year from each kW of roof-mounted, south-facing panels,[3] so 10,356 ÷ 1,595 = 6.49 kW.
- Panels: divide watts by the panel rating. 6,493 W ÷ 410 W = 15.8, so 16 panels (6.56 kW, about 10,463 kWh a year).
The 410 W panel is the module NREL's cost benchmark uses: 1.97 square meters (about 21.2 square feet) at 20.8% efficiency.[4] Panels on new home systems are now slightly more efficient, a median of 21.3% in 2025,[5] so check the rating on your quote.
How many solar panels to power a house
An average American home bought 863 kWh a month in 2024, but state averages differ widely: about 500 kWh a month in California and Hawaii, about 1,100 in Texas and Florida and about 1,200 in Louisiana.[1] Use your own bills. This table shows the 410 W panels needed to cover 100% of several usage levels in the lowest-, middle- and highest-output cities in our PVWatts table:
| Use per month | Houston, TX (1,421 kWh/kW) | Denver, CO (1,595 kWh/kW) | Phoenix, AZ (1,755 kWh/kW) |
|---|---|---|---|
| 500 kWh | 11 (4.5 kW) | 10 (4.1 kW) | 9 (3.7 kW) |
| 750 kWh | 16 (6.6 kW) | 14 (5.7 kW) | 13 (5.3 kW) |
| 863 kWh (U.S. average) | 18 (7.4 kW) | 16 (6.6 kW) | 15 (6.2 kW) |
| 1,000 kWh | 21 (8.6 kW) | 19 (7.8 kW) | 17 (7.0 kW) |
| 1,250 kWh | 26 (10.7 kW) | 23 (9.4 kW) | 21 (8.6 kW) |
| 1,500 kWh | 31 (12.7 kW) | 28 (11.5 kW) | 26 (10.7 kW) |
| 2,000 kWh | 42 (17.2 kW) | 37 (15.2 kW) | 34 (13.9 kW) |
The median home system installed in 2025 was 7.7 kW,[5] about 19 of these panels. Your location may produce less than the cities listed; PVWatts gives the figure for your own address, which you can enter in the calculator. The national lab's U.S. mean capacity factor of 15.7% works out to about 1,375 kWh per kW.[6]
Worked example: solar panels for 1,000 kWh per month
A home using 1,000 kWh a month (12,000 a year) needs about 19 panels of 410 W near Denver and 21 near Houston. Panel wattage changes the count, not the system size:
| Panel rating | Panels | System size | Panel area |
|---|---|---|---|
| 350 W | 22 | 7.70 kW | 398 sq ft |
| 380 W | 20 | 7.60 kW | 393 sq ft |
| 410 W | 19 | 7.79 kW | 403 sq ft |
| 430 W | 18 | 7.74 kW | 400 sq ft |
| 450 W | 17 | 7.65 kW | 396 sq ft |
Panel area here scales with wattage at constant efficiency. Your installer's layout decides the real footprint.
Will the panels fit on your roof?
At 21.2 square feet per panel, 16 panels cover about 339 square feet before spacing and fire-code setbacks. On homes with solar installed in 2025, panels typically covered 16% to 39% of the total roof area.[5] Roofs facing south get the most; about half of all panels faced south in 2024 and 22% faced west.[5] If the roof is near the end of its life, replacing it first avoids removing the panels later; the roof replacement cost calculator estimates that job.
Covering less than 100%Where your utility credits exported power at less than retail, a system that covers only the power you use during the day can pay back faster than one that covers the whole year. Set the share below 100% and compare paybacks in the solar calculator.
From panel count to cost
A 6.56 kW system at the 2025 median installed price of $3.60 per watt costs about $23,616 before incentives.[5] Price your own size with the solar panel cost calculator, and if you will borrow for it, compare a HELOC and other loans with the home improvement loan calculator. Household use figures come from EIA, which notes that purchases understate consumption in homes that already have solar.[2]
Frequently asked questions
How many solar panels do I need for my house?
Panels = yearly kWh ÷ local kWh per kW ÷ panel kW. For the U.S. average of 863 kWh a month near Denver: 16 panels of 410 W (6.56 kW).
How many solar panels for 1,000 kWh a month?
About 19 panels of 410 W near Denver (1,595 kWh per kW per year), more where the sun is weaker.
How much roof space do solar panels need?
About 21.2 square feet per 410 W panel, plus spacing and setbacks. 16 panels take about 339 square feet.
How many kWh does a solar panel produce?
A 410 W panel near Denver makes about 654 kWh a year, or 54 kWh a month (PVWatts).[3]
Sources
- Electric Sales, Revenue, and Average Price, Table 5A: 2024 Average Monthly Bill, Residential
- How much electricity does an American home use?
- PVWatts V8 API (annual output per kW at each city, queried November 13, 2026)
- U.S. Solar Photovoltaic System and Energy Storage Cost Benchmarks, Q1 2023 (NREL/TP-7A40-87303)
- U.S. Distributed Solar and Storage: 2026 Data Update (Tracking the Sun)
- Annual Technology Baseline 2025: Residential PV