1. Break the roof into planes
Sketch the roof from above and divide it into simple shapes: rectangles for most gable and shed planes, triangles and trapezoids for hip ends. Label each plane so you can record its dimensions and pitch separately.
Include porches, garages and additions only if they are part of the job. A clear plane list makes it easy to show the customer which surfaces are in the scope.
2. Measure footprint and pitch
From the ground or from imagery, measure each plane’s horizontal dimensions, including overhangs at the eaves and rakes. Measure pitch as rise over 12 inches of horizontal run, with a level and tape on a safe surface, a pitch gauge, or an aerial measurement.
Horizontal area of a rectangle is length × width; a triangle is base × height ÷ 2; a trapezoid is (top + bottom) ÷ 2 × height. Keep these as horizontal (projected) areas until the next step.
3. Correct for slope and add the planes
Multiply each plane’s horizontal area by its pitch factor: 4:12 ≈ 1.054, 5:12 ≈ 1.083, 6:12 ≈ 1.118, 8:12 ≈ 1.202, 10:12 ≈ 1.302, 12:12 ≈ 1.414. Example: a 40 × 15 ft horizontal plane at 6:12 is 600 × 1.118 ≈ 671 square feet of roof surface.
Add every sloped plane for the total roof surface, then divide by 100 for squares. If a measurement is already slope-corrected, such as a FastRoofReport surface area, do not multiply by the pitch factor again.
4. Waste, bundles and edge materials
Add a waste allowance as a separate line, then divide the planned area by the bundle coverage printed on the product wrapper and round up. Many asphalt shingle lines are packaged at about three bundles per square, but coverage varies by product.
Shingles are only part of the order. Record eaves and rakes for drip edge and starter, ridges and hips for ridge cap, and valleys for valley material. The roof edge guide explains each edge type.
Worked example: a simple gable roof
Example data: a gable roof with two equal planes, each 40 ft long at the eave and 15 ft of horizontal run from eave to ridge, including overhang, at 6:12 pitch. Horizontal area is 2 × 40 × 15 = 1,200 sq ft. Sloped surface is 1,200 × 1.118 ≈ 1,342 sq ft, or about 13.4 squares.
With a 10% example waste allowance the planning area is about 1,476 sq ft. At 33⅓ sq ft per bundle that is 1,476 ÷ 33.33 ≈ 44.3, so 45 bundles of field shingles. Edges: 80 ft of eave, 4 rakes of about 16.8 ft each (15 × 1.118) and a 40 ft ridge for starter, drip edge and ridge cap.
Measure from the ground, from plans or from imagery wherever possible. Do not climb a roof just to take these measurements.
Sources & further reading
Product details reflect FastRoofReport’s current measurement and report workflow. Geometry examples are rounded illustrations, not measurements of the pictured property.