Roofing Calculator
Use this roofing calculator to estimate roof surface area, roofing squares and approximate shingle bundles for a simple gable roof. Enter the building footprint, roof pitch and waste allowance to convert horizontal area into sloped roof area.
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Planning estimate only. Confirm local prices, supplier specifications and site conditions before ordering.
Your estimate
Simple footprint-and-pitch math is useful for planning, but complex roofs should be broken into individual planes and measured carefully before ordering.
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How the roofing calculator works
Roof area = footprint area × pitch factor. Pitch factor = √(1 + (rise ÷ 12)²). Roofing squares = roof area ÷ 100, with waste applied before bundle quantity.
For a better estimate
- This simple model works best for uncomplicated gable roofs. Valleys, hips, dormers and multiple roof sections should be measured separately.
- Use actual roof dimensions where possible rather than relying only on interior floor area.
- Roofing work can be dangerous; use professional measurement methods or contractor estimates when safe access is not available.
Tools that can help with this project
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Frequently asked questions
How do I calculate roof square footage?+
Start with the horizontal footprint, multiply by a pitch factor and measure complex roof sections separately.
What is a roofing square?+
One roofing square equals 100 square feet of roof surface area.
How much waste should I add for shingles?+
Waste depends on roof complexity, shingle layout and cuts. Simple roofs generally need less than roofs with many valleys, hips or penetrations.