WebCalculus

Roofing Calculator

Calculate roofing squares, shingle bundles and material cost for any roof size.

Flat Roof Area (sq ft)
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Actual Roof Area (sq ft)
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Roofing Squares
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Bundles of Shingles
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Rolls of Underlayment
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Estimated Material Cost
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Planning a roof replacement? Get quotes from local contractors for installation costs.

How the Roofing Calculator Works

This roofing calculator starts with the flat footprint area — length times width times number of faces. It then multiplies by the pitch multiplier to get the actual sloped roof area (a 6/12 pitch multiplier of 1.118 means the actual surface is 11.8% larger than the flat footprint). A waste factor (typically 10%) is added for cuts, hips, valleys and ridges. The result is divided by 100 to get roofing squares — the standard unit used by roofers. Standard three-tab asphalt shingles require 3 bundles per square. Underlayment rolls cover approximately 4 squares each. Material cost is calculated from bundle count times your price per bundle.

Frequently Asked Questions

How many shingles do I need per square foot of roof?
It takes 3 bundles of standard asphalt shingles to cover 1 roofing square (100 sq ft). Each bundle covers about 33 sq ft.
What is a roofing square?
A roofing square equals 100 sq ft of roof surface. Roofers price and order materials by the square.
How do I calculate the area of a roof with pitch?
Multiply the flat footprint area by the pitch multiplier. A 6/12 pitch multiplier is 1.118, so a 1,000 sq ft footprint = 1,118 sq ft of actual roof area.
How much does a new roof cost per square?
Professionally installed asphalt shingles typically cost $350–$500 per square installed, depending on region and complexity.

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