From a satellite measurement to a material order: perimeter, slope and waste
Eaves and rakes feed drip edge and starter, hips and ridges feed cap, valleys feed metal and ice & water, and area × pitch × waste becomes bundles. A worked hip roof.
A satellite measurement becomes a material order through three numbers: the edge lengths by type, the pitch, and your waste factor. Eave and rake footage turns into drip edge and starter, hips and ridges into cap, valleys into valley metal and ice & water, and plan area × pitch factor × waste into squares and bundles.
The trace gives you the perimeter and every edge length once it's labeled. Slope you bring yourself. Waste is your call. Here's how each lands on the order, then one full roof to check with a calculator.
Perimeter: every edge feeds a line
Once each edge carries a label, the perimeter stops being one number and splits into the runs a supplier ships against:
| Measured edge | Order line | How it converts |
|---|---|---|
| Eave + rake | Drip edge | Footage ÷ stick length less the lap |
| Eave (+ rake if you start it) | Starter | Footage ÷ lf per bundle |
| Ridge + hip | Hip & ridge cap | Footage ÷ lf per bundle |
| Valley | Valley metal, ice & water | Footage ÷ piece or roll length |
| Eave | Ice & water band | Footage × courses ÷ roll length, where code requires it |
A hip roof has little or no rake, so its drip edge is almost all eave. And a shared edge between two facets is one valley or one hip, counted once. Double-label it and you double the metal.
The trace and the labels are covered step by step in how to measure a roof from satellite imagery.
Slope: plan area isn't the roof
Satellite imagery is shot from above, so the trace gives you plan area: the footprint at the drip edge. A pitched plane is bigger than its footprint. Multiply by the pitch factor, the square root of (1 + (rise ÷ 12)²): 1.054 at 4/12, 1.118 at 6/12, 1.202 at 8/12.
Pitch comes from a site visit, the job file, or a street-level photo run through our free pitch finder. Slope stretches hips and valleys too: they run on the diagonal and climb, so a hip on a 6/12 roof is 1.5 times its run.
Waste: on the field, then round once
Waste covers off-cuts in the field: courses cut at hips, valleys and rakes. Put it on shingles, the nails that follow them, and underlayment. Linear lines start at straight footage; adding waste there is caution, not a rule. Pick the percentage from your worst section of roof, not the average. Our waste factor guide by roof type has starting ranges.
Then squares to bundles: true area × (1 + waste) ÷ 100 = squares, and standard 3-tab and architectural shingles typically run 3 bundles a square. The wrapper wins if it says otherwise. Round each line up once, at the end, in the unit the yard sells.
A worked example: hip roof with a gable wing
The roof: a 52 × 32 ft hip roof traced at the drip edge, with a 22 ft wide front gable wing projecting 18 ft, all at 6/12. The measurement reads:
- Plan area: 52 × 32 + 22 × 18 = 1,664 + 396 = 2,060 sq ft
- True area: 2,060 × 1.118 = 2,303 sq ft, or 23.0 squares
- Eaves: 182 lf. Rakes: 25 lf (the wing's gable end)
- Hips: 96 lf (four at 24 ft). Ridge: 49 lf (20 ft main, 29 ft wing)
- Valleys: 33 lf (two at 16.5 ft, open metal)
Waste is 12%, the middle of the gable + hip bracket. Coverage figures are assumptions; swap in the ones on your wrapper.
| Measured | Material | Quantity |
|---|---|---|
| 2,303 sq ft true area, 12% waste | Shingles, 3 bundles a square | 2,303 × 1.12 = 2,579 sq ft = 25.79 sq × 3 = 77.4 → 78 bundles |
| 2,579 sq ft with waste | Synthetic underlayment, 1,000 sq ft a roll net | 2.58 → 3 rolls |
| 182 lf eave + 25 lf rake = 207 lf | Starter, 105 lf a bundle | 1.97 → 2 bundles |
| 207 lf eave + rake | Drip edge, 10 ft sticks with a 2 in. lap | 207 ÷ 9.83 = 21.1 → 22 sticks |
| 96 lf hip + 49 lf ridge = 145 lf | Hip & ridge cap, 25 lf a bundle | 5.8 → 6 bundles |
| 33 lf valley, two runs of 16.5 ft | Valley metal, 10 ft pieces | 2 a valley → 4 pieces |
| 182 lf eave + 33 lf valley = 215 lf | Ice & water, 36 in. × about 66 lf a roll, one course | 3.26 → 4 rolls |
| 26 squares of shingles (78 ÷ 3) | Coil nails, 66 shingles × 4 nails = 264 a square, 7,200 a box | 26 × 264 = 6,864 → 1 box for the field, 2 with starter and cap |
Three lines deserve a second look before you send it.
Starter. 2 bundles cover 210 lf against 207 lf of edge: 3 ft of slack. Lose one piece and you're short, so take a third.
Ice & water. One course at the eave is the minimum shown here. Where code requires two courses, the eave run doubles: 182 × 2 + 33 = 397 lf ÷ 66 = 6.02 → 7 rolls.
Nails. Where the wrapper calls for 6 nails a shingle, the field count becomes 10,296: 2 boxes before starter and cap.
Pipe boots and step flashing don't come off the edge lengths. Count the boots by size and step flashing per wall. How to build a roofing material order from a measurement covers those lines and the delivery details the yard needs.
Where RoofStruct fits
RoofStruct gives you free, unlimited self-serve measuring and PDF reports, no card. You trace on satellite imagery or your own drone or phone photo, and the PDF on any plan lists the lengths by edge type: eaves, rakes, hips, ridges and valleys, plus a Length Diagram with each segment. That's everything in the left column of the table above.
On Pro, the Material Order Builder fills the order lines from that measurement at the waste % saved on it, and Smart Waste suggests the percentage from the roof's geometry. Every line stays editable before it goes to your supplier.
Where you trip
- Ordering off plan area. 2,060 sq ft of footprint is 2,303 sq ft of roof at 6/12. That's 2.4 squares, 8 bundles after waste, gone.
- Rakes on a hip roof. A plain hip has none. If the measurement shows rake footage on a four-sided hip, a label is wrong.
- Waste on every line by habit. It's a choice on linear lines. Know which lines carry it before you compare two orders.
- Assuming ice & water coverage. How far up the eave it runs is the manufacturer's and local code's call. Check before you count rolls.
FAQ
How many bundles of shingles are in a square?
Typically 3 for standard 3-tab and architectural shingles. Heavier lines can take more, so read the wrapper.
Do hips and ridges use the same cap?
Usually, yes: one hip & ridge cap line covers both, so add the footage before you divide. Ridge vent runs on the ridge only, so keep that footage separate.
Can a satellite measurement give me pitch?
No. An overhead image shows plan area, not rise. Get the pitch on site, from the job file, or from a street-level photo, then apply it per facet.
Does underlayment get the waste factor?
It gets cut at hips and valleys too, so carrying the field waste onto it is common. On the example roof it's 3 rolls either way.