How Accurate is Satellite Roof Measurement? (With Real Tests)
We measured 12 Australian roofs using satellite imagery and compared to physical tape measurements. Here's the accuracy, error sources, and when you can trust the numbers.
Short answer: ±1–2% on a typical Australian house — provided you apply pitch correction. That's well inside the tolerance you need for a roofing or solar quote. Here's what we found when we actually tested it.
The test setup
12 residential roofs across Sydney, Melbourne, and Brisbane. Each measured two ways:
- Satellite measurement in RoofMate, with pitch confirmed from Street View
- Physical tape measurement on the day of inspection (two roofers, averaged)
Roof types: 4 gable, 4 hip, 2 skillion, 2 mixed (gable + hip).
Results
- Mean absolute error: 1.4% of total roof area
- Best case (simple gable, 20° pitch): 0.3% error
- Worst case (complex hip with multiple dormers): 3.1% error
- 10 of 12 roofs landed within ±2%
- No roof exceeded ±4%
Where the error comes from
Imagery resolution
Google Maps imagery in Australian metro areas is around 6 cm/pixel. The edge of a roof is rarely a single pixel wide — there's a transition zone of 2–3 pixels. On a 10 m edge, that's ~0.2% perimeter error.
Pitch estimation error
Reading pitch from Street View is accurate to about ±2°. At 25° pitch, that translates to ±0.5% on the pitch factor. Multiplied across the whole roof: ~0.5% area error.
Eaves and overhangs
A 30 cm eave on a small extension can be confused with the wall line in satellite view. This is the biggest single source of error on small roofs.
Image age
If the imagery is 3+ years old and the property has had an extension, your measurement will be wrong by the difference. Always check the imagery date and cross-reference with Street View.
When satellite measurement is NOT accurate enough
- Hail repair claims — insurance wants tape-measured certified numbers
- Heritage roofs with irregular geometry that doesn't resolve at 6 cm/pixel
- Very small jobs (<20 m²) where 2% error is more than 1 panel or 1 sheet
- Buildings under construction — imagery may be obsolete by the time you measure
How RoofMate keeps you on the accurate side
- Imagery date displayed in the corner of every map
- Snap-to-vertex (Shift while drawing) eliminates the "wobbly polygon" error
- Pitch correction built into the Properties panel
- Edge-length labels on each segment so you can sanity-check against site notes
- Multi-tool overlays — overlay your traced polygon on Street View for verification
Try RoofMate free for 7 days and measure your next roof both ways — you'll be surprised how close the satellite number lands.
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