🏠 Roofing Calculator
Enter your roof’s footprint and pitch, and get the true sloped area, the number of roofing squares and shingle bundles to order.
Shingle bundles
4
1.3 squares incl. waste
Roof area
113.8 sq ft
slope factor ×1.054
With waste
127.5 sq ft
Roof area = footprint × √(1 + (rise/12)²). 1 square = 100 sq ft ≈ 9.29 m², usually 3 shingle bundles. Add ~10–15% for ridges/valleys. 🔒 In your browser.
How the roofing calculator works
A pitched roof is larger than its footprint. The tool multiplies the footprint area by a slope factor — √(1 + (rise/run)²) — to get the true roof area, then converts to roofing squares (100 sq ft each) and shingle bundles (typically 3 bundles per square).
Add ~10–15% for waste, ridge caps, valleys and starter courses. This estimates one plane by footprint × slope factor; for complex roofs, add up each section. Always follow the shingle manufacturer’s coverage.
Frequently asked questions
How do I calculate roof area from the footprint?
Multiply the footprint area by the slope factor √(1 + (rise/run)²). A 4/12 pitch has a factor of about 1.054, so a 100 m² footprint is about 105 m² of roof.
What is a roofing square?
A unit of roof area equal to 100 square feet (about 9.29 m²). Roofing materials are often quoted per square — asphalt shingles usually come 3 bundles to the square.
How many bundles of shingles do I need?
Divide the roof area by 100 sq ft to get squares, then multiply by 3 bundles per square (check your product). Add 10–15% for waste, ridges and valleys.
What is roof pitch?
The steepness, given as rise over a 12-unit run (e.g. 4/12 rises 4 inches per 12 across). Steeper pitches mean more roof area for the same footprint.
How much extra should I order?
About 10% for a simple gable roof and up to 15% for hips and valleys, plus starter and ridge-cap shingles.
Related home & DIY tools
From the blog
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Roof Pitch Explained: 4/12 in Degrees, Walkability, and Minimum Slopes by Material
Roof pitch is rise per 12 inches of run — a 4/12 roof rises 4 inches every 12 across, which is 18.4°. Here's the pitch-to-degrees chart, which roofs are safe to walk, and the minimum slope asphalt shingles and tile actually require.
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How Many Shingles Do I Need? Roofing Squares and Pitch Explained
A roof is bigger than its footprint because it slopes. Multiply the footprint by the slope factor √(1 + (rise/run)²), convert to roofing squares (1 square = 100 sq ft), then to shingle bundles (usually 3 per square). Worked examples and how much to add for waste.