Roofers
Roofing Calculator
Calculate roofing squares and shingle bundles needed for any roof size and pitch.
40′ × 30′ footprint × 1.118 pitch multiplier = 1342 sq ft actual roof area = 13.4 squares. With 15% waste: 15.4 squares × 4 bundles = 62 bundles. Starter strip, ridge cap, and flashing ordered separately.
How to calculate roofing materials
Roofing is measured in squares. One roofing square is 100 square feet. To figure out how many squares you need, measure the footprint of the roof and multiply by the pitch factor. A 2,000 square foot footprint with a 6/12 pitch works out to about 2,236 square feet of actual roof area, or about 22.4 squares. This calculator does the pitch conversion for you.
How many bundles of shingles per square?
Standard three tab shingles come 3 bundles to a square. Architectural shingles vary. Some are 3 bundles per square, others are 4 or 5 depending on the weight and style. Check the bundle label for the manufacturer's coverage spec. This calculator factors in the shingle type so you get the right bundle count.
Do not forget underlayment and ridge cap
Every roof needs underlayment, and most reroofs need ice and water shield in the valleys and along the eaves. A roll of synthetic underlayment covers about 10 squares. Ice and water shield covers about 2 squares per roll. Ridge cap is sold by the linear foot or in bundles. Measure your ridge length and hip lengths to figure that number. These extras add up fast if you do not plan for them.
Waste factor for roofing
Plan for 10 to 15 percent waste on a standard gable roof. Hip roofs generate more waste because of the angle cuts at the hips and valleys. Complex roofs with a lot of valleys, dormers, and angles can run 15 to 20 percent waste. It is always better to have a few extra bundles on the job than to be short and have to wait for a delivery.
Common Questions
How long does a roof last?
Standard asphalt shingles last 20 to 25 years. Architectural shingles go 25 to 30 years. Metal roofing can last 50 years or more. Weather, ventilation, and installation quality all play a role.
Can you roof over existing shingles?
Most codes allow one layer of new shingles over old. But tearing off is almost always better because you can inspect the deck for rot. Two layers also adds weight and traps heat that shortens the new roof's life.
What is the best time of year to replace a roof?
Late spring and early fall are ideal. Shingles seal best between 45 and 85 degrees. Summer works too but it is brutal on the crew. Avoid roofing in winter if you can since shingles get brittle in the cold.
How long does it take to reroof a house?
A typical 2,000 square foot home takes 1 to 3 days for a tear off and reshingle. Complex roofs with lots of valleys and dormers can take longer. Bad weather pushes everything back.
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