Finding roof pitch from satellite imagery and Street View
Why a top-down image can't show pitch, how to read it from Street View or a gable-end photo, the pitch-factor table from 3/12 to 12/12, and what a two-step miss costs.
You can't read roof pitch from satellite imagery, because a top-down image shows plan area and no rise. Get the pitch from a street-level view instead: face a gable end on Street View and match the rake to a pitch line, or use a gable-end photo, a level on a rake, or the homeowner's plans.
Then apply it per facet. Pitch moves squares more than most tracing mistakes.
Why satellite imagery can't show pitch
From straight above, a 4/12 plane and a 10/12 plane with the same footprint look identical. The rise runs toward the camera, so it never shows up in the picture.
Shadows give you a hint, not a number: they change with the time of day, the season and which way the house faces. Overhead imagery gives you the footprint and line lengths. Pitch has to come from the side.
The Street View method, step by step
Street View shows the house from the road, which is the side view you need. Our free roof pitch finder puts 12 pitch lines over Google Street View so you can read the rake against them:
- Enter the address. Street View opens facing the house.
- Face a gable end. Turn until you look straight at a gable end or a roof edge. A rake seen at an angle looks flatter or steeper than it is.
- Keep the view level and zoom in. Look straight ahead, not up or down, or the lines tilt against the roof.
- Match a line. Drag the view until one of the pitch lines lies along the rake. Tap a pitch label to highlight its line and check the fit.
In RoofStruct's builder, the Street View button opens the same tool on the project's address. No street photo, or trees over every gable? Use another method.
Other ways to get pitch
A gable-end photo. Stand back, zoom in and shoot the gable square-on. On screen, measure the rise from eave to peak and the run from the eave to the center of the gable, in the same units. Pitch = rise ÷ run × 12. A rise of 140 pixels over a run of 290 pixels is 140 ÷ 290 × 12 = 5.8, so call it 6/12.
A level and tape on a rake. Hold a level flat with one end on the roof surface, measure 12 inches out along it, then measure straight down from that mark to the roof. That number in inches is the rise per 12.
A smartphone inclinometer app. Lay the phone on the roof surface and read the angle in degrees. Convert it with the table below.
The homeowner's plans. Elevations usually mark pitch with a small triangle and a rise over 12. Additions don't always match the original set.
The pitch-factor table
Pitch factor = the square root of (1 + (rise ÷ 12)²). Multiply plan area by it to get true area.
| Pitch | Angle | Pitch factor | 1,000 sq ft plan becomes |
|---|---|---|---|
| 3/12 | 14.0° | 1.031 | 1,031 sq ft |
| 4/12 | 18.4° | 1.054 | 1,054 sq ft |
| 5/12 | 22.6° | 1.083 | 1,083 sq ft |
| 6/12 | 26.6° | 1.118 | 1,118 sq ft |
| 7/12 | 30.3° | 1.158 | 1,158 sq ft |
| 8/12 | 33.7° | 1.202 | 1,202 sq ft |
| 9/12 | 36.9° | 1.250 | 1,250 sq ft |
| 10/12 | 39.8° | 1.302 | 1,302 sq ft |
| 11/12 | 42.5° | 1.357 | 1,357 sq ft |
| 12/12 | 45.0° | 1.414 | 1,414 sq ft |
What a two-step miss costs
Take a 46 × 28 ft gable house with a 1 ft overhang. Traced at the drip edge, the roof is 48 × 30 ft, or 1,440 sq ft of plan area. The real pitch is 7/12.
- At 7/12 (correct): 1,440 × 1.158 = 1,668 sq ft, or 16.7 squares. With 10% waste, 18.3 squares, so 55 bundles at 3 per square.
- Read as 5/12: 1,440 × 1.083 = 1,560 sq ft, or 15.6 squares. With waste, 17.2 squares, so 52 bundles. You're 108 sq ft and 3 bundles short.
- Read as 9/12: 1,440 × 1.250 = 1,800 sq ft, or 18.0 squares. With waste, 19.8 squares, so 60 bundles. You're 132 sq ft and 5 bundles over.
The rakes move too. Each one covers 15 ft of run, so it's 15 × 1.158 = 17.4 ft at 7/12 and 16.2 ft at 5/12. Four rakes, and the drip edge comes up almost 5 ft short.
One predominant pitch or a pitch per facet
In RoofStruct, the Pitch card sets a predominant pitch, and every facet inherits it until you select the facet and give it its own. On a simple gable or hip roof, one pitch is the whole job. A porch, a dormer or a second pitch needs per-facet pitch. How to measure a roof from satellite imagery covers the split.
Some contractors skip the predominant setting and pitch every facet by hand. When every facet has its own pitch, the project page and the PDF show a predominant pitch anyway: the pitch that covers the most plan area, with same-pitch facets added together. That's display only. The area and squares are still calculated from each facet's own pitch. If any facet is left without a pitch, the predominant pitch shows a dash and that facet's area is counted flat until you fix it.
RoofStruct offers free, unlimited self-serve measuring and PDF reports, no card. New to the builder? Measure your first roof in RoofStruct walks through the screens.
Where you trip
- Reading the rake at an angle. A corner view distorts the slope. Face the gable square-on.
- Tilting the view. Looking up from the curb skews every line.
- One pitch for a mixed roof. The porch at 3/12 and the main roof at 8/12 can't share a number.
- Leaving a facet unpitched. It's counted flat, and the order comes up short.
FAQ
Can you get roof pitch from a satellite image?
No. An overhead image shows the footprint, not rise. Get pitch from a street-level view, a photo, a level or the plans.
How accurate is the Street View method?
Square-on to a gable, level and zoomed in, you get a good read. Corner angles, trees and old street photos make it harder. Measure on site when pitch decides the job.
How do I convert degrees to pitch?
Pitch = tan(angle) × 12. A 30° reading is tan(30°) × 12 = 6.9, so call it 7/12.
Does a steeper pitch change the squares?
Yes. True area is plan area times the pitch factor. On 1,440 sq ft of plan area, 5/12 gives 15.6 squares and 9/12 gives 18.0 squares.