Start from sloped surface area
Use the measured roof surface, not the house floor area or the footprint. A 1,600-square-foot house with overhangs and a 6:12 roof can easily have well over 2,000 square feet of roof surface.
One square is 100 square feet. Write the measured squares down first, then add waste as a separate step so the estimate shows both numbers.
Worked example
Measured surface: 2,000 sq ft (20 squares). Waste allowance: 10%, giving 2,200 sq ft. Bundle coverage from the wrapper: 33⅓ sq ft. 2,200 ÷ 33.33 = 66.0, so order 66 bundles.
At 15% waste, the same roof is 2,300 sq ft and 69 bundles. Complex roofs with many hips, valleys and dormers usually need more allowance than a simple gable; agree the figure with your installer and supplier.
Starter and ridge cap are separate
Starter: eave length, plus rake length where the manufacturer requires it, divided by the linear feet per starter bundle. Ridge cap: ridge plus hip length, divided by the linear feet per ridge cap bundle.
Linear coverage differs widely between products, so read it from the actual package. Cutting field shingles for starter or ridge changes the field shingle count.
Use measurements you can trust
A small error in area multiplies through every bundle. Check that the measurement includes the right buildings and that unusual flat or steep facets are real.
RoofSnap reports give surface area, pitch and edge totals for $6.99, and the material calculator turns them into quantities for several shingle lines. Confirm final quantities before ordering.
Sources & further reading
Product details reflect RoofSnap’s current measurement and report workflow. Geometry examples are rounded illustrations, not measurements of the pictured property.
Google Solar API documentation