Roof Space Calculator: How Many Solar Panels Fit on Your Roof

How Many Solar Panels Fit on a Typical UK Roof?

Spirit Energy says 8 to 12 solar panels fit on each unobstructed roof face of "many three-bed semis", roughly 3.2 to 5.4 kWp with 400 to 450 W panels (Spirit Energy blog, read 8 November 2026). kWp (kilowatt peak) is the rated power of the panels added up: the watts printed on each panel's datasheet, times the number of panels, divided by 1,000.

How many panels fit is a different question from how many solar panels you need, which starts from the electricity your house uses in a year. Switch Together puts a 4 kWp system at around 10 to 12 panels on "roughly 26 m² of clear roof space" (Is Your Roof Suitable for Solar Panels?, 26 January 2026). Both are those sites' figures, not our measurements.

Your own number rests on five things: the width and slope length of each roof face, the clearance kept from its edges, the space taken by chimneys and roof windows, the panel size, and which way round the panels go. The calculator above works through all of them except chimneys and roof windows. A typical figure does not describe your own roof, so here is one roof face worked through.

Worked Example: One Roof Face on a Typical Semi

One 7.5 m by 5.13 m roof face holds 10 panels of 1,762 x 1,134 mm at the MCS edge clearance of 400 mm, and 12 if your installer gives you a 200 mm clearance and a 30 mm gap. The face is our illustration, not a measured average: no source we hold gives the roof size of a typical semi. The calculator opens on this face.

At the MCS clearance the 10 panels cover 19.98 m² of the 29.01 m² usable area. The rest is strips too narrow for a whole panel. That is why dividing the area by the size of one panel gives too high a count. The smaller clearance adds 2 panels even with the gap counted. The third row shows why the gap matters: with no gap counted, the 200 mm clearance gives 16, 4 more than with the gap. The example used four measurements and one layout rule. The next section sets out the method.

How Do You Work Out How Many Solar Panels Fit?

To work out how many solar panels fit, measure each roof face, take off the edge clearance, then count how many whole panels fit in rows and columns. The rows and columns on one face make up the solar array. The method has five steps.

1. Measure each face: the width along the eaves and the length up the slope, from the eaves to the ridge.
2. Take the edge clearance off all four sides of the face.
3. Leave out the parts of the face that chimneys, roof windows and vents take up.
4. Count the whole panels that fit across and up, with any gap between panels, in portrait and in landscape, and keep the layout that holds more.
5. Multiply the panels by the watts of one panel and divide by 1,000 to get the kWp.

The calculator does steps 2, 4 and 5 for up to four faces and names the layout it kept. For step 3 you enter the clear part of each face. Step 4 needs the space one panel takes, which the next section gives. Work out the panels that fit your roof

How Much Roof Space Does One Solar Panel Need?

One solar panel of 1,762 x 1,134 mm needs 2.00 m² of roof space, before any gap between panels. Of the 9 datasheets in our records, 8 give that panel size (length and width), for panels of 425 W to 495 W; one gives 1,722 x 1,134 mm, which covers 1.95 m². Switch Together gives a smaller figure, "around 1.6 m²" for a standard panel (26 January 2026).

A more efficient panel puts more watts into the same size, so the same roof holds a bigger system in kWp. It does not make each kWp generate more kWh: in our calculation the same kWp gives the same yearly output whatever the panel's efficiency. Panel dimensions, weight and wattage across more makers are compared in our guide to solar panel sizes and wattage.

How Much Roof Space Do You Need per kWp?

As a rule of thumb, allow 4.0 to 4.7 m² of panel per kWp with 1,762 x 1,134 mm panels of 425 W to 495 W (our calculation from the datasheets). Then add the gaps between panels and the edge clearance around them. Published guides give other figures, and the table shows what each one counts.

Use the rule of thumb to check a quote, then let the layout give the real count: the example face has 29.01 m² of usable area and holds 4.25 to 4.95 kWp. Both rules start from a measured roof face.

How to Measure Your Roof Without Going Up on It

Measure the width of each roof face from the ground, along the wall under its eaves, and work out the length up the slope from the depth of the roof and its pitch. Stay off the roof: the Energy Saving Trust says "It's always safer to avoid working at heights if you don't have the right training or equipment" (updated 1 October 2026).

• Width: the run of the eaves, measured along the wall below the face.
• Length up the slope: the calculator asks for the slope, not the depth you see from below. The slope is the depth divided by the cosine of the pitch, so our example face, 7.5 m wide and 4.2 m deep at a 35 degree pitch, is 5.13 m up the slope. Work this out before you type it in.
• Obstacles: note each chimney, roof window and vent, and where it sits on the face.

Whether the roof suits solar at all is a separate check, which our roof checker for direction, pitch and shade covers. At the survey, an installer measures the roof for the quote. With the faces measured, the next choice is which way round the panels go.

Portrait or Landscape: Which Fits More Panels?

Whichever leaves less wasted space on your face, so try both. On the 7.5 m by 5.13 m example face at the 400 mm MCS clearance, portrait fits 10 and landscape 9. With a 200 mm clearance and a 30 mm gap, both fit 12; with no gap, landscape fits 16 and portrait 12 (our calculation).

The calculator works out both and keeps the layout with more panels, all one way round on each face, and the result card names it. Any layout uses only the space left after the clearance and the obstacles.

What Reduces the Number of Panels That Fit?

Three things take space away from a clear roof face: the edge clearance, obstacles, and the shape of the roof. Shade does not stop a panel from fitting, but it lowers what that panel generates. The Energy Saving Trust says optimisers stop one shaded panel affecting the others. The edge clearance comes first.

Edge Margins: How Far From the Roof Edge?

MCS sets 400 mm from any edge as the margin for a home's roof: "Solar PV modules should not be mounted within 400mm from any edge of a domestic roof unless specific measures are taken" (MIS 3002 Issue 6.0, dated 18 March 2026, clause 5.9.7). The measures it names include keeping the ridge tiles secure.

The calculator uses 400 mm and takes it off all four sides of every face, including a hip or valley where two faces meet. That is our reading of "any edge". An installer who takes those specific measures may work closer to the edge, so you can type the clearance they give you and the card says the MCS figure is not used. On the 7.5 m by 5.13 m example face, moving this edge setback from 400 mm to 200 mm, with a 30 mm gap, takes the count from 10 to 12 panels. Obstacles on the face are the next thing to measure around.

Chimneys, Dormers, Roof Windows and Vents

A chimney, roof window (skylight) or vent takes its own footprint out of the face, plus whatever gap your installer leaves around it. So measure the clear part of the face: our calculator does not take obstacles off. Its position on the face matters, as well as its size. One at the edge may fall inside the clearance already; one in the middle of the face splits the rows.

For a face split by an obstacle, enter each clear part as its own face. The calculator then takes the clearance off every side of each part, so the count comes out low. Your installer's layout sets the real gap. A dormer is a roof of its own: Sunsave's roof checklist says dormer space is "not usually designed to support the weight of panels" (26 June 2026). The shape of the whole roof matters too.

Hipped, L-Shaped and Other Complex Roofs

A hipped or broken-up roof holds fewer whole panels than its area suggests, because a face that narrows towards the ridge has less room for a full rectangle of panels. The calculator treats each face as a rectangle, so for a hipped face enter the largest rectangle that sits inside it, and for an L-shaped roof enter each straight run as its own face. MCS counts a design with "increased potential for snow build-up (e.g. dormers, valleys, parapets etc)" as an unusual roof. For an unusual roof, its standard says "a qualified structural engineer shall be consulted". A small or broken-up face can be topped up with a second face.

Can You Use More Than One Roof Face?

Yes. The calculator adds up to four faces, so an east and a west slope, or a main roof and a garage, count together. Direction does not change how many panels fit, but it changes what they generate: at a 35 degree pitch, a face facing east makes 79.5% and one facing west 78.9% of what the same face makes facing south (our calculation from PVGIS 5.3).

A north-facing face makes 54.2% of the south figure, and our panel count calculator gives a north-facing roof a Poor fit verdict. Roof direction and its effect on output are covered in our guide to the best orientation for solar panels.

A garage, carport or outbuilding roof can go in as another face. Our garage illustration, a 5.5 m by 2.7 m roof, holds 4 panels (portrait, 4 across by 1 up), which takes the example roof from 10 to 14 panels. Whether that roof suits panels at all is the subject of our guide to solar panels on a garage or outbuilding.

On a flat roof, the Energy Saving Trust says panels are "normally tilted up", many of them "weighted down rather than fixed through the roof covering". The calculator lays panels flat on each face and has no setting for frames. Space is one limit on the count, and the next section sets out three more.

Limits That Are Not About Space

There is no fixed number of panels you are allowed, but three things can stop you filling the space: planning rules, the rules for connecting to the electricity network, and the strength of your roof.

• Planning: in England, panels on a pitched roof count as permitted development only if they sit no higher than the highest part of the roof (chimney excluded) and stand no more than 200 mm from the slope. The house must not be listed (Planning Portal, rules from 27 August 2026).
• Connection: under the Energy Networks Association's G98 rule, a system of up to 16 A per phase (3.68 kW on a single-phase supply) is notified to your Distribution Network Operator (DNO), the company that runs the local electricity network. Above that, the G99 process applies, and the DNO needs to be consulted before the installation.
• Structure: MCS says the roof structure is to be "checked by a suitably competent person", and each panel on our datasheets weighs 21.1 kg to 24.6 kg.

Once you know what fits and what is allowed, the next question is whether to use all of it.

Should You Fill Your Roof With Solar Panels?

Only if the extra panels pay their way. Compare the panels that fit with the panels your home needs, then check the cost and payback of each size before you decide. The result card links to the panel count calculator with your count. That calculator works from your yearly electricity use (2,500 kWh unless you change it).

Bigger systems cost less per kWp. The DESNZ domestic retrofit mean is £2,109 per kWp up to 4 kWp and £1,651 from 4 to 10 kWp (DESNZ Solar PV cost data, domestic retrofit installations, April 2025 to March 2026). Electricity you do not use is exported through the Smart Export Guarantee (SEG), at 13p per kWh by default (our calculation from Ofgem figures). The SEG started on 1 January 2020. It is not the Feed-in Tariff, which closed to new applicants on 1 April 2019. A fuller roof can also pass the G98 limit and need a G99 application.

The figures on this page are for an example face, and your own roof changes the result. To see the cost of what fits on your roof, run the size through the main calculator, which shows the saving and payback too. The next section sets out how our tool reaches its numbers.

How We Work Out What Fits on Your Roof

We lay out whole panels in rows and columns inside the edge clearance on each face you enter, both ways round, and keep the layout with more panels. Each input has a source.

• Edge clearance: 400 mm from MIS 3002 Issue 6.0, dated 18 March 2026, clause 5.9.7, taken off all four sides of each face; or your installer's figure.
• Panel size: 1,762 x 1,134 mm or 1,722 x 1,134 mm, from the 9 datasheets in the table above, or a size you type.
• kWp: panels x the watts you type / 1,000, or a range across the datasheets of that size.
• Gap between panels: none, unless you type your installer's figure, because no source we hold gives a fixed gap.
• Example face: 7.5 m by 5.13 m, our illustration of 8 November 2026, not a typical roof.

The card shows the usable area and the area the panels cover, in m², so you can compare them with a quote. The calculator does not model obstacles, faces that are not rectangles or the depth seen from the ground. The result card names the clearance and panel size it used. A survey replaces our measurements with the installer's.

Get a Free Survey to Measure Your Roof

At a survey, an MCS-registered installer measures your roof, designs the panel layout and then gives you a quote. You request one after a Good fit or Borderline result in our panel count calculator, in four steps.

The survey request form on this site is not open yet.

You will get phone calls. That is how surveys are arranged. There is no obligation, and you can withdraw at any time. We are paid by Leads 2 Trade Limited when a homeowner we refer asks for a survey. You are never charged. It does not change our figures.

With a roof space result in hand, you can request a home survey from MCS-registered installers to have the roof measured. We do not refer tenants, people who are just researching, homes in postcodes outside the installers' coverage, people shopping for plug-in solar, or households eligible only for funded schemes. The request form is not open on this site yet. The next questions about the same roof are how much electricity the panels would generate and what the system would cost.

What Would a System That Fills Your Roof Cost?

Our calculator prices both a 4 kWp and a 5 kWp system at £8,400, fitted at 0% VAT, from the DESNZ domestic retrofit mean cost for April 2025 to March 2026. The example face holds 4.25 to 4.95 kWp, between the two sizes. Home solar carries 0% VAT until 31 March 2027 and 5% from 1 April 2027 (HMRC VAT Notice 708/6). At 5% VAT, each comes to £8,800. Prices for other counts, with or without a battery, are in our guide to solar panel cost by number of panels.

Roof Space Questions