How to measure a roof from a phone photo (no drone)
A phone photo from the driveway can't be traced for area, but it gives you the pitch, the overhang and the details a satellite view hides. What to shoot and how to use it.
A phone photo taken from the ground cannot be traced for roof area: the view is oblique, every plane is foreshortened, and no two edges share a scale. What it gives you is the pitch, the overhang, the edge types and the details a satellite view hides, which are exactly the numbers a satellite footprint is missing. Pair the two and you can order from the result without a drone or a ladder. The one exception is a shot taken from above the roof, which you treat like a drone photo.
What a ground-level phone photo can and can't give you
The footprint comes from the trace in our satellite measurement guide, or from a tape around the walls. The phone photo fills in the rest.
| Number | From the phone photo? | Where it comes from |
|---|---|---|
| Footprint (eave to eave) | No | Satellite trace, or walls plus overhang |
| Pitch | Yes, from a gable end | Rise over run on the photo, or the free pitch finder |
| Overhang | Yes | A tape from the wall to the fascia, photographed |
| Edge types (hip, rake, valley, step wall) | Yes | One shot per side of the house |
| Vents, chimneys, skylights | Yes | Close shots of each |
| Roof area | Computed | Footprint × pitch factor |
The trap is making the photo do the first row: a tape on the lawn is 30 ft closer to the lens than the far corner of the roof, so any scale taken from it is wrong before you reach the ridge.
The five shots to take
One walk around the house, in daylight, main camera rather than the ultrawide lens, roof near the middle of the frame where phone lenses distort least.
- A gable end, square on. Stand on the centreline of the gable, as far back as the lot allows, phone level, camera grid on. This is the pitch shot.
- Each eave with a tape from the wall to the fascia. One shot per side that has a different overhang; porches and additions often differ.
- Each side of the house. For edge types: where a hip replaces a rake, where a valley meets the main roof, where a slope dies into a wall.
- Every penetration, close. Pipe boots, box vents, ridge vent, chimney and cricket, skylights. The satellite view shows a dot; the photo shows what the dot is.
- The lower roofs. Porch, bay window, garage. A low roof under the main eave is often half hidden from above.
Pitch from the gable-end shot
On the gable photo, find the rake from an eave corner to the ridge, and a horizontal from that corner to the point directly under the ridge. The horizontal is the run (half the gable width); the vertical from the corner up to the ridge is the rise. Measure both on screen in any unit. Rise divided by run, times 12, is the pitch: a rise of 2.6 over a run of 5.2 is 6/12. Round to the nearest common pitch; the photo is not better than half a pitch either way.
Two things throw it off. Standing off the centreline foreshortens the gable sideways, shrinks the run, and makes the pitch read steeper than it is. Tilting the phone up to fit the roof in makes the verticals converge and the rise read short. Stand back instead of tilting, and square instead of close. The fascia should run dead horizontal across the frame; if it slopes, move.
If you cannot get square to a gable, or would rather not drive out, the free roof pitch finder does the same thing on Street View: face the gable and match it to one of 12 pitch lines. Our pitch guide has the pitch factor table you need next.
Footprint: the satellite trace plus your overhang
Trace the roof outline on satellite imagery, eave to eave, and you have the footprint including the overhang. The photo of the tape at the fascia is your check: subtract the overhang from each side and compare with the wall dimensions from the permit, the listing or your tape. If the outline is 40 ft and the walls tape 38 ft with a 12 in overhang each side, the trace is right. If they disagree by more than a foot, the imagery is leaning and you trust the tape.
The same walk catches the lower roof the satellite hid. A porch roof tucked under the main eave is a sliver from above and a full plane from the sidewalk; trace it as its own facet with its own pitch.
When the phone is above the roof
Sometimes you can get the phone higher than the eave without a drone: an upstairs window across the street, a hillside lot, a camera pole, a ladder at the eave of a one-storey shed. If the shot looks down at something close to straight down, it is a usable overhead image and the rules switch to our drone photo guide: lay a tape or a measured board flat and in frame before you shoot, so the image carries one known length, and keep the roof centred.
A second-storey window is usually oblique enough that only the near slope is worth tracing; treat it as a check on the satellite trace, not a replacement. In RoofStruct, a satellite view is scaled automatically; an uploaded photo needs that one known length drawn once.
A worked bungalow
A plain gable bungalow, ridge running the long way.
- Satellite trace, eave to eave: 40 ft × 28 ft, a 1,120 sq ft footprint.
- Tape at the fascia: 12 in overhang all round, so walls of 38 ft × 26 ft, matching the listing.
- Gable shot: rise 2.6 over run 5.2 on screen, so 6/12. Pitch factor 1.118.
- Roof area: 1,120 × 1.118 = 1,252 sq ft, or 12.5 squares before waste.
- Eaves: 2 × 40 = 80 ft of drip edge and starter.
- Rakes: half-width 14 ft, so each rake is 14 × 1.118 = 15.7 ft, and four come to 62.6 ft.
- Ridge: 40 ft of cap, or ridge vent if the close shot showed one.
- Penetrations: two pipe boots, one box vent, no chimney.
No length was traced off the photo, and the list is enough to price and order.
Where you trip
- Scaling the eave off a tape on the lawn. The tape and the eave sit at different distances from the lens. The scale only holds on the plane the tape lies in.
- Shooting the gable from the corner of the lot. Off-axis reads steep. If the fascia is not horizontal in the frame, move.
- Assuming one overhang. Additions, porches and garages were built at different times. Photograph each.
- Forgetting the pitch of the lower roofs. The gable photo gives the main pitch. A porch or a shed dormer needs its own.
FAQ
Can I measure roof area from a phone photo taken from the ground?
No. The view is oblique, so there is no single scale across the image. Get the footprint from a satellite trace or a tape, the pitch from the gable photo, and multiply.
Is a phone photo good enough to get the pitch?
Yes, to within about half a pitch, if you stand square to the gable with the phone level.
Do I need a drone if I already have a satellite view?
Usually not. A satellite trace plus a gable shot and an overhang shot covers a standard re-roof. A drone earns its place when the imagery is old, trees hide the roof, or the roof is too cut up to read from above.