Roofing Calculator

Calculated using standard mathematical and industry formulas.

Calculate total roof area, roofing squares, and required asphalt shingle bundles based on building footprint and pitch slope.

How to use this calculator?

1. Enter house footprint.
2. Select pitch.
3. Read roofing squares and shingle bundles.

Formula & calculation method

Pitch Multiplier Model

Roof Area = Footprint × Pitch Multiplier

Pitch slope multiplier.

Step-by-step calculation example

40x30 footprint @ 4/12 = 14.5 squares with waste.

Key insights to remember

• 1 Square = 100 sq ft.
• 3 bundles = 1 square.

How to interpret your results?

Roofing Squares

Unit for purchasing shingles.

Frequently asked questions

What is a roofing square?

A roofing square is a unit of area equal to 100 square feet of roof surface.

How many bundles of shingles are in a square?

Standard 3-tab and architectural asphalt shingles require exactly 3 bundles per square (100 sq ft).

What waste percentage should I add for roofing?

Use 10% waste for simple gable roofs, 15% for hip roofs with valleys, and up to 20% for complex roofs.

How is roof pitch calculated?

Roof pitch is expressed as inches of vertical rise per 12 inches of horizontal run (e.g., 4/12 pitch).

How many rolls of felt underlayment do I need?

Standard #15 felt covers ~4 squares (400 sq ft) per roll, while synthetic underlayment covers ~10 squares (1,000 sq ft).

Should overhangs be included in the measurement?

Yes, add 1 to 2 feet to footprint dimensions to account for eave and rake overhangs.

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