Solar system size calculator: how many panels for my house?
Take the monthly kWh from your electric bill and the yearly output per kW of panels for your area. The calculator gives the system size in kW and how many panels that is.
Enter your measurements
More options: Offset
- Panels
- 18 panels · 400 W
- Expected output per year
- 10,894 kWh
- Average output per month
- 908 kWh
- Your use per year
- 10,356 kWh
863 kWh × 12 = 10,356 kWh a year
÷ 1,513 kWh per kW a year = 6.84 kW of panels
6,845 W ÷ 400 W = 18 panels
- PVWatts output assumes a south-facing array tilted at the latitude with no shade. East- or west-facing roofs and shade make less; run PVWatts with your own roof’s tilt and direction for a firmer number.
Quick answers for common sizes
| Example | Answer |
|---|---|
| How many solar panels for 1000 kWh per month | 7.93 kW — 20 × 400 W panels (Dallas) |
| How many solar panels for 2000 kWh per month | 15.86 kW — 40 × 400 W panels (Dallas) |
| How many solar panels to run an average house | 7.92 kW — 20 × 400 W panels (Chicago) |
The same home in other cities
| City | System size | Panels | Expected output per year |
|---|---|---|---|
| Phoenix, AZ | 5.8 kW | 15 panels | 10,722 kWh |
| Los Angeles, CA | 6.1 kW | 16 panels | 10,874 kWh |
| Denver, CO | 6.33 kW | 16 panels | 10,464 kWh |
| Miami, FL | 6.67 kW | 17 panels | 10,554 kWh |
| Dallas, TX | 6.84 kW | 18 panels | 10,894 kWh |
| Chicago, IL | 7.92 kW | 20 panels | 10,464 kWh |
| New York, NY | 8.01 kW | 21 panels | 10,861 kWh |
| Seattle, WA | 9.67 kW | 25 panels | 10,710 kWh |
Worked examples: how many solar panels for 1000 kWh per month, how many solar panels for 2000 kWh per month and how many solar panels to run an average house.
How the system size is worked out
system kW = monthly kWh × 12 × share to cover ÷ yearly kWh per kW panels = system kW × 1,000 ÷ panel watts
The key number is how much a kilowatt of panels makes in a year where you live. NREL’s PVWatts calculator (now run by the National Laboratory of the Rockies) models it hour by hour from long-term weather data, including heat, the inverter and its default 14% system losses. The figures in the location list come from PVWatts for a south-facing array tilted at each city’s latitude; for your own roof, run PVWatts at your address with your roof’s pitch and direction.
| City | kWh per kW a year | kW for 1,000 kWh/month | 400 W panels |
|---|---|---|---|
| Phoenix, AZ | 1,787 | 6.72 | 17 |
| Los Angeles, CA | 1,699 | 7.06 | 18 |
| Denver, CO | 1,635 | 7.34 | 19 |
| Miami, FL | 1,552 | 7.73 | 20 |
| Dallas, TX | 1,513 | 7.93 | 20 |
| Chicago, IL | 1,308 | 9.17 | 23 |
| New York, NY | 1,293 | 9.28 | 24 |
| Seattle, WA | 1,071 | 11.2 | 29 |
What the calculator doesn’t know
- Your roof. Orientation, pitch and shade change output a lot. An east or west roof makes less than south; shade from trees can make a big difference.
- Your utility’s rules. Net metering, export rates and system size limits decide whether covering 100% of your use makes financial sense.
- Future loads. An EV or heat pump adds a lot of kWh — the EV solar calculator estimates a car’s share; see how many solar panels to charge a Tesla Model Y for one example.
- Permits and codes. Grid-tied systems need permits, utility approval and code-compliant installation by licensed installers.
What you’ll need
- Plug-in electricity usage monitorBudget price
Plugs in between the wall and a 120 V appliance and shows real watts and kWh over a day — the honest way to fill in a load list, especially for fridges that cycle on and off.
See options on Amazon (opens in a new tab) - 400 W residential-size solar panelPremium price
Fewer, larger panels for a cabin, shed or ground mount. Their higher voltage usually means an MPPT controller.
See options on Amazon (opens in a new tab)
As an Amazon Associate we earn from qualifying purchases. Links to products are affiliate links — they cost you nothing extra and help keep these calculators free.
Frequently asked questions
How many solar panels do I need for 1000 kWh per month?
About 7.9 kW — twenty 400 W panels — at a Dallas-like 1,513 kWh per kW a year. In Phoenix about 6.7 kW, in Seattle about 11.2 kW. See how many solar panels for 1000 kWh per month.
How much electricity does an average house use?
In 2024 the average US residential customer used about 863 kWh a month (about 10,359 kWh a year), according to the EIA — with big differences by state: Louisiana averaged 1,202 kWh a month, Hawaii 495.
What is a kWh per kW figure?
How many kilowatt-hours one kilowatt of solar panels makes in a year at a given place. PVWatts gives about 1,787 in Phoenix and 1,071 in Seattle for a south-facing tilted array.
Can I use peak sun hours instead?
Yes, roughly: kWh per kW a year ≈ peak sun hours × 365 × 0.86. PVWatts’ own figure is usually a little lower because it also models panel heat and the inverter hour by hour.
Related guides
Sources
- National Laboratory of the Rockies (formerly NREL) — PVWatts® Calculator (opens in a new tab) — Look up the solar resource (peak sun hours) and yearly output for your own address; default system losses 14%.
- NLR (formerly NREL) — PVWatts® v8 API, NSRDB PSM V3 TMY data (opens in a new tab) — City figures on this site: fixed open-rack array facing due south, tilted at the site’s latitude, 14% system losses, queried October 2026.
- U.S. Energy Information Administration — Electric Sales, Revenue, and Average Price, Table 5A (2024 data, released October 2025) (opens in a new tab) — 2024 average residential customer: 863 kWh a month (about 10,359 kWh a year, 28.4 kWh a day); Louisiana 1,202 kWh a month, Hawaii 495.