Roof material roll estimator

Roof Underlayment Calculator

Estimate roofing underlayment rolls from roof footprint, pitch, roll coverage, and waste or overlap allowance. Use it with shingle or metal roofing takeoffs before ordering felt, synthetic underlayment, or ice-and-water membrane.

Units

Roof footprint length (ft)Roof footprint width (ft)Roof pitch rise per 12 Overlap / waste (%)Roll coverage (ft²)Cost per roll ($)

Rolls to buy

Underlayment area

Roof squares

Rough cost

Underlayment layout depends on roof details

Lap rules, starter courses, valleys, hips, ridges, eaves, penetrations, ice-dam zones, roof slope, manufacturer instructions, and local code can change roll counts. This is a material estimate, not a roofing specification.

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Roof Shingle Calculator

Estimate shingles, bundles, and waste for the same roof area.

Metal Roofing Calculator

Estimate metal panel rows and roof material cost.

Roof Pitch Calculator

Get the pitch multiplier and slope angle before estimating roof rolls.

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Roof underlayment formula

Pitch multiplier = √(1 + (pitch ÷ 12)²)

Sloped roof area = footprint length × footprint width × pitch multiplier

Order area = sloped area × (1 + waste/overlap %)

Rolls = order area ÷ roll coverage

Sample takeoff

A 30 ft by 40 ft roof footprint at 6/12 pitch has about 1,342 ft² of sloped area. With 15% overlap/waste and 1,000 ft² rolls, order about two rolls.A 9 m by 12 m roof footprint at 6/12 pitch has about 121 m² of sloped area. With 15% overlap/waste and 93 m² rolls, order about two rolls.

Roof Underlayment Calculator FAQ

How many square feet does a roll of roof underlayment cover?+

Common synthetic rolls often list about 1,000 ft² of gross coverage, but installed coverage changes with laps and product width. Use the coverage printed on the roll when ordering.Common synthetic rolls often list about 1,000 ft² of gross coverage, but installed coverage changes with laps and product width. Use the coverage printed on the roll when ordering.

Does this include ice-and-water shield?+

No. It estimates field underlayment from the dimensions you enter. Ice-and-water membrane depends on eaves, valleys, roof penetrations, climate, code, and product rules.No. It estimates field underlayment from the dimensions you enter. Ice-and-water membrane depends on eaves, valleys, roof penetrations, climate, code, and product rules.

Why add overlap or waste?+

Underlayment courses lap horizontally and vertically, and cuts around valleys, hips, vents, and edges use extra material. The overlap/waste input accounts for that loss.Underlayment courses lap horizontally and vertically, and cuts around valleys, hips, vents, and edges use extra material. The overlap/waste input accounts for that loss.