In short: Most homes need between 10 and 25 solar panels, but the right number depends on how much electricity you use, how much sun you get, and how powerful each panel is, not on the size of your house. To find your number, divide your annual electricity use (kWh) by your local solar yield (kWh per kW), then divide the resulting system size by your panel wattage.
Many websites answer this question with square footage alone, and that leads to bad estimates. A 2,000 sq ft (186 m²) home with an electric car and a heat pump uses far more power than the same home without them. This guide shows you how to size a system properly, with a simple formula, worked examples, and a reference chart.
The simple formula to calculate how many solar panels you need
Use these three steps:
- Find your annual electricity use in kilowatt-hours (kWh) from your utility bills.
- Divide by your local solar yield (kWh produced per kW installed per year) to get the system size in kW.
- Divide the system size by your panel wattage to get the number of panels.
Number of panels = (Annual kWh ÷ Solar yield) × 1,000 ÷ Panel wattage
If you’re not sure what a kilowatt or a kilowatt-hour is, read our guide to kW vs kWh and how to size a system from your energy bill.
Step 1: Find your annual electricity use
Look at your last 12 months of bills and add up the kWh, or check your utility’s online account, which usually shows your annual total. For reference, typical annual use is roughly:
- US: around 10,000–11,000 kWh per household.
- UK: around 2,700 kWh for a medium household (electricity only).
These are averages; your own bills are what matter. If you plan to add an electric vehicle, heat pump, or electric heating, add that expected use to your total (an EV can add roughly 3,000–4,000 kWh per year for average driving).
Step 2: Find your local solar yield
Solar yield tells you how many kWh a 1 kW system produces in a year at your location. It depends on sunshine, roof direction, tilt, and shading. Approximate ranges:
| Region | Typical yield (kWh per kW per year) |
|---|---|
| UK and northern Europe | 850–1,000 |
| US Northeast and Pacific Northwest | 1,100–1,300 |
| US Midwest and Mid-Atlantic | 1,200–1,400 |
| US Southeast and Texas | 1,350–1,550 |
| US Southwest (Arizona, Nevada, southern California) | 1,500–1,800 |
These are estimates for well-oriented, unshaded roofs. For a specific address, use a tool like NREL’s PVWatts (US) or ask installers for a site-specific production estimate.
Step 3: Calculate your system size
System size (kW) = Annual kWh ÷ Solar yield
Example: a US home using 10,500 kWh per year in a region with a yield of 1,400 kWh/kW needs 10,500 ÷ 1,400 = 7.5 kW.
Step 4: Convert system size into number of panels
Number of panels = System size (W) ÷ Panel wattage
Modern residential panels are typically 400–450 W. Using 400 W panels, the example above gives 7,500 ÷ 400 = about 19 panels. With 440 W panels, you’d need about 17.
Worked examples
| Home | Annual use | Yield | System size | Panels (400 W) |
|---|---|---|---|---|
| US home, Arizona | 12,000 kWh | 1,650 | 7.3 kW | ~18 |
| US home, Ohio | 9,000 kWh | 1,250 | 7.2 kW | ~18 |
| US home, Washington State | 10,000 kWh | 1,150 | 8.7 kW | ~22 |
| UK home, average use | 2,700 kWh | 900 | 3.0 kW | ~8 |
| UK home with EV and heat pump | 7,000 kWh | 900 | 7.8 kW | ~19 |
Notice how the same number of panels can serve very different homes: what drives the result is consumption and sunshine, not floor area.
How many solar panels by house size?
If you want a quick rule of thumb, here is a rough guide based on typical energy use for homes of different sizes and an average level of sun (about 1,300 kWh/kW). Treat it as an illustration, not a quote:
| House size | Typical panels (400 W) | Approx. system size |
|---|---|---|
| 1,000 sq ft (93 m²) | 5–9 | 2–3.5 kW |
| 1,500 sq ft (139 m²) | 8–13 | 3–5 kW |
| 2,000 sq ft (186 m²) | 12–18 | 5–7 kW |
| 2,500 sq ft (232 m²) | 15–22 | 6–9 kW |
| 3,000+ sq ft (279+ m²) | 18–28 | 7–11 kW |
These ranges are wide on purpose. Two homes of the same size can differ by 3x in electricity use.
Step 5: Check that the panels fit on your roof
A typical 400 W panel measures about 1.7 m × 1.1 m (roughly 5.6 ft × 3.6 ft), or around 1.9 m² (20 sq ft). So 19 panels need about 36 m² (390 sq ft) of usable, unshaded roof, not counting spacing, vents, chimneys, and fire-code setbacks. If your roof is too small, options include:
- Choosing higher-wattage panels to get more power from the same area.
- Using multiple roof faces (east and west can work well).
- Adding a ground mount or carport if you have space.
- Sizing the system to cover part of your usage instead of 100%.
Read more about roof direction and angle and solar panels on different roof types.
Factors that change how many panels you need
- Panel wattage: higher-wattage panels mean fewer panels for the same system size.
- Shading: trees and neighboring buildings can reduce output by 10% or much more, so you’d need extra capacity.
- Roof direction and tilt: a poorly oriented roof may need more panels for the same production.
- Your goal: covering 100% of your usage needs more panels than covering 60–80%. Sometimes a smaller system delivers a better payback.
- Future electricity use: if you plan to buy an EV or install a heat pump, size for the future.
- Battery storage: adding a solar battery changes how much of your solar you use directly, but not how many panels you need to generate the energy.
- Local rules: some utilities or regions cap system size at a percentage of your past consumption or limit export power.
- Efficiency losses: real-world losses from heat, wiring, and the inverter are already built into yield figures, but degradation of about 0.4–0.5% per year means output slowly declines over time.
Should you size for 100% of your electricity use?
Not always. Going from 70% to 100% offset often requires panels that produce mostly during midday, when you may be exporting to the grid at a lower rate than you pay to import. Whether it’s worth it depends on your net metering or export tariff, your daytime consumption, and whether you have a battery. A good installer should show you different system sizes and their expected savings.
Try the calculator
Want a quick estimate for your home? Use our solar savings calculator (choose your country to get local yield and pricing).
Next steps
- Gather your last 12 months of electricity bills.
- Calculate your rough system size with the formula above.
- Learn how a home solar system works so you can follow installer proposals.
- Compare quotes and spot red flags before signing.
Where to next:
Frequently asked questions
How many solar panels do I need to run my whole house?
Most homes need roughly 10–25 panels to cover their annual electricity use, depending on consumption, location, and panel wattage. To cover your specific needs, divide your annual kWh by your local solar yield, then by the panel wattage.
How many solar panels do I need for a 2,000 sq ft house?
Typically about 12–18 panels of 400 W, but it depends much more on your electricity use than on the size of the house. Use your bills to get an accurate figure.
How many solar panels do I need to power a house and an electric car?
An EV can add roughly 3,000–4,000 kWh per year, which usually means about 2–3 kW more solar capacity (roughly 5–8 additional 400 W panels), depending on your location and driving habits.
How many solar panels do I need without a battery?
The same number. A battery doesn’t change how much energy your panels generate; it only changes how much of it you can use at night or during outages.
Is it better to have more or fewer panels?
Not necessarily more. The best size balances your electricity use, roof space, budget, and how your utility credits exported energy. Oversizing can reduce your return if exports are paid at low rates.
How much roof space do I need for solar panels?
About 1.9 m² (20 sq ft) per 400 W panel. A typical 7 kW system needs roughly 32–40 m² (350–430 sq ft) of usable roof.