How many solar panels fit on your roof?
This calculator gives you a rough idea of how many solar panels will fit on your roof. Enter your address and it measures each section of your roof from Google’s aerial and 3D data, keeps panels 400 mm from the edges as the MCS installation standard advises, and then fits in as many rows as it can. You’ll get a panel count and system size for the two common panel sizes.
This calculator is only a guide. Its measurements aren’t exact, so have an installer measure your roof before you buy anything.
How it works
We find your house and measure each section of the roof from Google’s 3D height data: how big it is, how steep it is and which way it faces.
Panels go in upright rows from the gutter up, with a row on their side at the top if there’s room. They keep the gaps you set around the panels, which start at the 400 mm the MCS installation standard advises. Every section counts, north-facing ones too: they still make power, much of it from light scattered by cloud.
System size in kWp is panels × watts ÷ 1,000. Twelve 430 W panels make 12 × 430 ÷ 1,000 = 5.16 kWp.
Common questions
How accurate is it?
It’s an estimate to start conversations with installers. Aerial data can be a few years old and can differ from your roof. Always have an installer measure and check your roof before you buy.
Which panel size should I plan for?
We show the two common sizes, so you can compare. 1.7 m panels are usually 420 to 460 W each. 1.95 m panels are usually 480 to 520 W, so fewer fit but each one makes more. The wattages come from manufacturers’ datasheets.
What if it can’t find my house?
Type your house number, street and postcode, then pick your address from the list. If it isn’t there, type just your postcode and tap your house on the map, or press “Measure it myself instead” and type in the size of your sunniest roof section.
I live in a semi or a terrace. Does it count next door’s roof?
It might. If one of the orange sections on the map belongs to your neighbour, tap it to take it off. Tap it again to put it back.
Why don’t the shapes line up with my roof on the photo?
The photo is taken at a slight angle. The measurements come from 3D height data, not the photo, so they’re not affected.
Should panels go portrait or landscape?
It depends on the shape of your roof, and your installer will decide. This calculator fits as many upright (portrait) rows as it can, then adds a row on their side (landscape) at the top if there’s space.
Do I need planning permission for roof panels?
In England, usually not, if panels stay within 200 mm of the roof and below the ridge. Listed buildings, conservation areas and flats differ, and Wales and Scotland have their own rules. Ask your council if unsure.
How do I work out kWp from the number of panels?
Panels × watts ÷ 1,000. Twelve 430 W panels make 12 × 430 ÷ 1,000 = 5.16 kWp.
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