Roofing materials, counted before you climb
Start from the footprint and pitch, or from measured roof planes. Get squares with waste, shingle bundles, underlayment rolls, drip edge pieces, and starter and ridge cap.
Measure each plane on the roof surface: along the eave, and up the slope from eave to ridge. Triangles (hip ends): use half the eave length.
Bundles = roof area × (1 + waste) ÷ coverage per bundle, rounded up. Drip edge assumes 10 ft pieces lapped 2 in at joints. Starter and cap bundles use the linear feet per bundle you enter (105 ft is one common starter product); check the bundle you buy. Check every figure against the product's own coverage and install instructions.
To estimate shingles, multiply the roof's footprint, overhangs included, by the pitch multiplier to get roof area, divide by 100 for squares, and add waste: about 10% for a simple gable and 15% or more for hips and valleys. Architectural shingles usually come 3 bundles to a square. A 50 × 30 ft footprint at 6/12 is 16.77 squares, 56 bundles with 10% waste.
How to use the roofing calculator
Measure the roof
Footprint length and width with the pitch, or each roof plane measured on the surface.
Pick the products
Waste for the roof type, shingle coverage per bundle, underlayment roll size, edge lengths.
Read the order
Bundles, squares with waste, underlayment rolls, drip edge pieces, starter and cap.
What the roofing calculator does
Two ways to measure
Footprint × pitch multiplier, or measured planes (length × slope length × count).
Waste by roof type
10% simple gable, 12% with a few cuts, 15% hip, 20% cut-up roofs.
Bundle coverage
33.3 sq ft (3 per 100 sq ft) or 32.8 sq ft (3 per 98.4 sq ft), plus 4- and 5-bundle squares.
Edges filled for you
One click fills eaves, rakes, ridge and hips for a simple gable or hip roof.
Accessories
Underlayment rolls, 10 ft drip edge pieces lapped 2 in, starter and hip and ridge bundles.
- Roof area
- footprint × √(rise² + 144) ÷ 12, or Σ plane length × slope length
- Bundles
- roof area × (1 + waste) ÷ coverage per bundle, rounded up
- Underlayment
- Synthetic 10 squares per roll, #15 felt 4 (Owens Corning); same waste added
- Drip edge
- (eaves + rakes) ÷ 9.83 ft (10 ft pieces, 2 in laps), rounded up
- Accuracy
- Estimate only: check product coverage, local code and a site measurement
Roofing Calculator FAQ
How many bundles of shingles do I need?
Divide the roof area by 100 to get squares, add waste, and multiply by the bundles per square on the wrapper, usually 3 for architectural shingles. Owens Corning's Duration, for example, is 3 bundles to a square that covers 98.4 square feet, so check the coverage.
How much waste should I add for shingles?
Owens Corning calls 10% to 15% a good rule of thumb. Use the low end on a simple gable and more on hip roofs, valleys, dormers and short runs; very cut-up roofs can need 20%.
How do I measure a roof without climbing it?
Measure the house footprint plus overhangs from the ground, multiply by the pitch multiplier and you have the roof area. Confirm the pitch from the attic or a ladder at the eave, or use an aerial measurement report.
How much underlayment do I need?
Roughly the roof area plus waste, divided by the roll's coverage: synthetic underlayment is commonly 10 squares a roll and #15 felt about 4. On slopes from 2/12 to 4/12 the IRC requires double underlayment, so double it.
Do I need starter strip on the rakes?
Many installers run starter along the rakes as well as the eaves for a straight edge and better wind resistance, and some manufacturers' starter products are made for both. Follow the shingle's installation instructions.
How many pieces of drip edge do I need?
Add the eave and rake lengths and divide by the piece length less the overlap. With 10 ft pieces lapped 2 inches, as the IRC requires at minimum, each piece covers about 9 ft 10 in.
Where the numbers come from
- Owens Corning: DIY roofing tips (squares, slope factors, waste, bundles, underlayment rolls)
- Owens Corning: TruDefinition Duration shingles (3 bundles, 98.4 sq ft per square)
- Owens Corning: Starter Strip Plus data sheet (105 lineal feet per bundle)
- ICC: 2021 International Residential Code, Chapter 9 Roof Assemblies (R905.2.2, R905.2.8.5)
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