FREE SOLAR ROOF CALCULATOR
How Many Solar Panels Will Fit on Your Roof?
Search your address, trace your roof on the satellite map and see how many solar panels fit, the system size in kW and roughly how many kWh it would make a year. Works for any address in the world, in square feet or square metres. Free, no signup.
Updated 26 September 2026
The quick answer
A typical 440 W panel is about 69 by 44.5 inches (1.76 by 1.13 m), or 21 square feet. Once you allow for gaps and clearance around the edges, each panel needs around 28 square feet of roof. So a 1,000 square foot roof section facing the right way fits about 37 panels, which is roughly 16 kW. Most homes run out of well facing roof, or budget, well before they run out of space.
Solar panels per roof size
This table uses the same assumptions as the calculator: a 20° roof pitch, 75% of the surface usable and 440 W panels. The area is the footprint of the roof section as seen from above, which is what you'd measure on a map.
| Roof section (from above) | Metric | Panels | System size |
|---|---|---|---|
| 250 ft² | 23 m² | 9 | 4.0 kW |
| 500 ft² | 46 m² | 18 | 7.9 kW |
| 750 ft² | 70 m² | 27 | 11.9 kW |
| 1,000 ft² | 93 m² | 37 | 16.3 kW |
| 1,500 ft² | 139 m² | 55 | 24.2 kW |
| 2,000 ft² | 186 m² | 74 | 32.6 kW |
How to measure your roof on the satellite map
- Type your address or ZIP code into the search box and zoom right in.
- Tap each corner of a roof section in order. Tap near your first corner, or press Close this section, to finish it.
- Repeat for any other roof faces you'd put panels on. Skip the ones facing away from the sun.
- Drag any corner to fine tune the shape, then enter your roof pitch and panel wattage.
- Switch between square feet and square metres whenever you like, and use Copy link to send the result to an installer.
Why the footprint isn't the whole story
A satellite photo shows the roof from directly above, which makes a sloped roof look smaller than it is. The calculator corrects for that using your pitch: a 4/12 roof (18°) is about 5% bigger than its footprint, a 6/12 roof (27°) about 12% and an 8/12 roof (34°) about 20%. Not sure of yours? Measure it from a photo with the free roof pitch calculator.
Direction matters as much as size. Panels facing the equator (south in the USA and UK, north in Australia) make the most, east and west faces make roughly 80% to 87% as much at a typical pitch, and the other side of the roof makes less again. Our solar panel angle calculator shows how a given roof face stacks up, and the roof azimuth calculator tells you exactly which way it faces.
How much power will the panels make?
Once you've searched an address, the calculator loads a typical year of weather for that spot and estimates yearly output for the system size you've drawn, assuming the panels face a good direction. As a guide, each kW of well placed panels makes about 1,370 kWh a year in New York, 1,700 in Los Angeles, 940 in London and 1,580 in Sydney. The solar orientation comparison goes further, with season by season output for each roof face.
How accurate is this?
The satellite measurement is accurate to within a couple of per cent if you place the corners carefully, as long as the imagery is recent. The panel count is deliberately conservative: a real layout depends on panel orientation, rail runs, local fire code setbacks and the obstructions on your roof, and that's the installer's job. Use it to sanity check quotes and to see whether your roof can take the system size you have in mind.
Common questions
How many solar panels can I fit on my roof?
Take the area of the roof faces you'd actually use, allow about 75% of it for panels once you leave room for edges, ridges and vents, then divide by the size of one panel: about 21 square feet (2 m²) for a typical 440 W panel. A 1,000 square foot south facing roof section fits roughly 37 panels, about 16 kW. The calculator above does this for your actual roof from a satellite photo.
How much roof space do I need for solar panels?
Around 28 square feet (2.6 m²) of roof per panel once setbacks and gaps are included, so a 6.6 kW system of 15 panels needs about 420 square feet (40 m²) and a 10 kW system of 23 panels about 650 square feet (60 m²).
Is my roof area the same as my home's floor area?
No. A single storey home's roof footprint is a little bigger than its floor area because of the eaves, and a two storey home has about half. The sloped surface is bigger again: a 6/12 pitch adds about 12%. Only the roof faces that point the right way are worth counting, which is why it's better to draw them on the map.
Do you store my address or roof outline?
No. There's no database behind this tool. If you use the Copy link button, the shape lives in the link itself, so only people you share it with can see it.
Does it subtract skylights, vents and fire setbacks?
Not individually. Either draw around them, or let the built in 75% usable factor cover them. In the USA many areas require clear access pathways along ridges and roof edges for firefighters; your installer will know the local rule, and it can cut the panel count on small or complicated roofs.
Can I measure a commercial or flat roof?
Yes, and it works well because commercial roofs are big and simple to trace. Set the pitch to 0 and keep in mind panels on flat roofs usually go on 10° to 15° frames with rows spaced apart to avoid shading each other, so the real count is lower than a pitched home roof of the same size.
Add this calculator to your website
Run a solar blog, an installer site or a sustainability page? You're welcome to embed this solar roof calculator for free. Copy the code below into any page. It works on WordPress, Squarespace, Wix and plain HTML, and there's nothing to sign up for.
Please keep the credit line under the calculator. If you need a different size or have a question, contact us.
Planning a system this size?
Once it is on the roof, the question changes from how many panels fit to whether every one of them is working. PV Fleet watches your system and alerts you within hours when a fault appears.