Roofing Calculator
Turn your house footprint and roof pitch into roof surface area. A 40 x 30 ft house with a 6/12 pitch has about 1,503 sq ft of roof, or 15.03 squares.
How roof area is calculated
A sloped roof has more surface than the floor plan beneath it. Take the footprint including overhangs and multiply by the pitch multiplier, which is the square root of 1 plus (rise / 12) squared. A 6/12 roof has a multiplier of 1.118.
Your example: (40 + 2) x (30 + 2) x 1.118 = 1,503 sq ft, which is 15.03 squares. With 10% waste you order 16.53 squares or 50 bundles. At $450 per installed square the job is about $7,438.06.
Typical roofing costs
Asphalt shingle roofs commonly cost $350 to $550 per square installed, metal $800 to $1,500 and tile $1,000 to $2,000. Steep or cut-up roofs cost more because of extra labor and waste.
This works for simple gable or hip roofs. For complex roofs, measure each plane separately and add them. See our shingle calculator if you already know the roof area.
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Frequently asked questions
How do I calculate roof area from the house size?
Multiply the footprint (with overhang) by the pitch multiplier. A 6/12 roof multiplies the footprint by about 1.118.
What is a roofing square?
One square is 100 square feet of roof surface.
How much does a new roof cost?
A typical asphalt shingle roof costs $350 to $550 per square installed, so about $8,000 to $15,000 for an average home.
How much waste should I allow?
10% for simple roofs, 15% or more for hips, valleys and dormers.
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