- Home
- Roof size calculator
Roof size calculator
Measure any South African roof in m² from its address.
Type the address and the roof appears from above. Where Google's aerial model covers it, you get the measured roof area at once. Outline the whole roof or one section and the area follows the pen. Free, no sign-up, works on a phone.
How does the calculator work out roof area?
Two measurements, and you can use either.
1. The measured roof
For most metro addresses Google's aerial model already holds the roof's surface area. The calculator shows that figure in m² as soon as the address is found.
2. Your outline
Tap the corners of the roof, or of one section, on the satellite picture. The area inside the outline is worked out from the map scale, and you can drag any corner to correct it.
3. More than one area
A house and a garage, or two wings of a factory, can be outlined separately. The calculator adds them together.
Why is roof area bigger than floor area?
Two reasons: the roof overhangs the walls, and it slopes. The slope is the part people forget. Sheet area equals the flat area divided by the cosine of the pitch.
| Roof pitch | Multiply flat area by | Sheet area |
|---|---|---|
| 5° (low-slope sheeting) | 1.004 | 100 m² |
| 15° | 1.035 | 104 m² |
| 22.5° | 1.082 | 108 m² |
| 30° | 1.155 | 115 m² |
| 35° | 1.221 | 122 m² |
Worked example: a 150 m² single-storey house, 10 m by 15 m, with 600 mm eaves all round has a flat roof footprint of 11.2 m × 16.2 m = 181 m². At a 15° pitch that is about 188 m² of sheeting.
Who uses a roof measurement?
- Homeowners pricing a re-roof. Roofing is quoted per m², so the area is the first number any contractor asks for.
- Solar installers. Panel count starts with usable roof area. Where the aerial model covers the address, the calculator also shows how many panels the roof could carry.
- Estate agents and home inspectors. A roof area on the listing or the report lets a buyer price a replacement before making an offer.
- Body corporates and facilities managers. Outline each block separately and get one total for the budget.
If the roof is fibre cement laid before 2008, the same three steps carry on to an asbestos removal estimate at R150 to R250 per m². If it is not, the area is yours to use anywhere.
Questions people ask about measuring a roof
How do I calculate the size of my roof in m²?
Type the street address into the calculator. It shows the roof from above, and where Google's aerial model covers the address it gives the measured roof area straight away. You can also outline the roof, or one section of it, on the picture and the calculator works out the area of the outline in m².
Is roof area the same as the floor area of the house?
No. A roof is bigger than the floor under it, because it overhangs the walls and because it slopes. A 15° pitch adds about 3.5% to the flat area, 22.5° adds about 8% and 30° adds about 15.5%. A 150 m² single-storey house with 600 mm eaves and a 22.5° pitch carries roughly 196 m² of sheeting.
How accurate is measuring a roof from a satellite picture?
Good enough for an estimate, a budget or a first quote, and not a substitute for a tape measure. Every quote for roof work should be fixed only after the roof has been measured on site.
Does the calculator work for any address in South Africa?
Yes. The address search and the satellite view cover the whole country. The automatic roof measurement depends on Google's aerial model, which covers most metro suburbs; where it does not, outline the roof by hand and the area is worked out from the map scale.
What does it cost to use?
Nothing. There is no sign-up and no email is needed to see the area. Details are only sent anywhere if you choose to send them.
To get a roof's size in m², type the address above. The calculator returns Google's measured roof area where it exists, and the area of any outline you draw where it does not. Between a 15° and a 35° pitch, roof area runs about 4% to 22% above the flat area, before eaves are counted. Use the figure for a budget or a first quote; a fixed price follows a measurement on site.