Roofing Calculator

Choose the mode that matches what you already know: your building's footprint and roof pitch (Simple Roof), a total roof area from a report or prior measurement (Measured Area), or several distinct roof sections you can measure separately (Multiple Roof Planes) — a main roof, a garage, an addition.

Your building's footprint is the flat area you'd measure from directly above. A pitched roof's actual surface area is larger than its footprint, because the sloped surface covers more area than its flat projection — the steeper the pitch, the bigger the difference.

Pitch is commonly expressed as x:12 (rise per 12 units of run), as an angle in degrees, or as a percentage — this calculator accepts all three and converts between them automatically. The pitch multiplier — √(x² + 12²) ÷ 12, equivalent to 1 ÷ cos(angle) — converts a flat, projected area into the actual sloped surface area. A 6:12 pitch has a multiplier of about 1.118; a 12:12 (45°) pitch has a multiplier of about 1.414.

All three roof types use the same underlying formula — extended footprint × pitch multiplier — and differ only in which overhang extends which edge. A hip roof with the same footprint, pitch, and overhang as a gable roof has the identical field (shingle) area, because the formula depends only on the footprint and the pitch, not on how the planes are arranged into hips versus a ridge. A hip roof typically needs more hip-and-ridge cap material and can warrant a higher allowance, since it has more angled cuts — but the underlying roof area calculation is the same.

Overhang is measured horizontally, in plan view — not along the slope — and extends the footprint before the pitch multiplier is applied. Eave overhang extends the edges below the roof's slope (all four edges for a hip roof); rake overhang extends the gable ends and doesn't apply to a hip roof, which has none.

A roofing square is 100 ft² — a standard roofing-industry planning unit, used regardless of material. This calculator shows your roofing-material figure as a decimal number of squares (for example, 19.25 squares) for easy communication with a supplier or contractor. It is always calculated from square feet, even in Metric mode, and is never rounded up to a whole purchase quantity — that's what bundle or package planning is for.

A 10% material allowance is a common planning baseline for a simple roof. More complex rooflines — hips, valleys, dormers, or many penetrations — commonly need more, since they require more angled cuts and produce more unusable offcuts. This allowance is fully editable; there is no single figure that's correct for every roof.

Three bundles per square (about 33.3 ft² per bundle) is common for standard 3-tab and many architectural shingles, but it is not universal — heavier laminate, designer, and luxury shingle products are often packaged 4 or 5 bundles per square. This calculator never assumes a bundle coverage for you: enter your product's actual coverage, or use the labeled ~33.3 ft²/bundle shortcut only as a starting point to verify against your specific product.

Synthetic underlayment commonly covers around 1,000 ft² (10 squares) per roll, while traditional felt covers less per roll and varies by weight. Coverage still varies by product, so enter your product's stated roll coverage rather than relying on a single assumed number for every roll.

Ridge-cap and starter-strip quantities depend on a length measurement — the total ridge and hip length for ridge cap, and the total eave (and sometimes rake) length for starter strip — that this calculator does not derive from your roof area or Simple Roof geometry. Measure the actual length and enter it directly, along with your product's coverage per package, to get a result.

In Multiple Roof Planes mode, add one section per distinct roof plane and enter it either from horizontal dimensions and pitch, or directly from a measured slope length — whichever you actually know for that section. Every plane's area is summed at full precision, and only then is the material allowance applied once to the combined total.

• Required roof pitch, structural design, or framing.
• Ice & water shield, flashing, or ridge vent.
• Nails, fasteners, or drip edge quantity.
• Soffit or fascia material — see the Soffit Calculator.
• Labor, contractor markup, or delivery.
• Building code or manufacturer installation compliance.

Follow your project drawings, manufacturer installation instructions, and a qualified professional for all of the above — this calculator estimates roofing material quantity only.