Roof Pitch Calculator: How to Estimate Pitch from Satellite Photos

Pitch is the one variable that turns a satellite area into a real roof area. Get it wrong and you under-quote by 10–20%. Here's how to estimate pitch accurately from imagery alone, plus the pitch factor table you'll actually use.

What is roof pitch?

Pitch is the angle of the roof slope, expressed either as degrees (most of the world) or as a ratio of rise over run (e.g. "4/12" — four inches of rise per twelve inches of run, common in older Australian and US practice). A 4/12 pitch is roughly 18°. Most Australian houses sit between 15° and 30°.

Why pitch matters for satellite measurement

Satellite imagery is taken straight down. A pitched roof appears smaller in plan view than it actually is. Multiply the plan area by a pitch factor to get the real surface area you need to quote on.

Pitch factor table (use this)

• 0° (flat): factor 1.000
• 10°: factor 1.015
• 15°: factor 1.035
• 20°: factor 1.064
• 25°: factor 1.103 — most common in Australia
• 30°: factor 1.155
• 35°: factor 1.221
• 40°: factor 1.305
• 45°: factor 1.414

Formula: plan area × factor = surface area. Example: 200 m² satellite area × 1.103 (25°) = 220.6 m² actual roof.

How to estimate pitch from satellite imagery

1. Open the address in Google Street View

The fastest method. Drag the Pegman onto the street outside the property. Rotate to face the gable end of the roof. The triangle you see — base over height — gives you the pitch directly.

2. Measure the gable triangle

Hold a pencil up to the screen and measure the base and the height of the gable triangle in millimetres. Then: arctan(height ÷ half-base) = pitch in degrees. RoofMate's Properties panel does this calculation for you if you click the two ends of the gable line.

3. Read shadows for cross-validation

Satellite imagery is shot at a known sun angle. The length of the shadow cast by the ridge line correlates to roof height. RoofMate's Height Estimation tool combines this with a known landmark for a quick sanity check.

Common Australian pitch ranges by roof style

• Federation / Queenslander tin roofs: 22°–30°
• Modern colorbond gable: 20°–25°
• Tiled hip roof (post-2000 estates): 22°–27°
• Skillion / mono-pitch contemporary: 5°–15°
• Heritage gabled brick (pre-1940): 25°–35°
• Flat / low-slope commercial: 1°–5°

Why this matters for solar quoting

Solar panels need a minimum tilt for self-cleaning and optimal generation (Australian recommendation: 15°–35° depending on latitude). If a roof is too flat, you need tilt frames, which add $50–$100/panel. Pitch directly drives the BOM, not just the install cost.