Roof Area & Material Calculator

Roof area and material take-off

From horizontal plan to sloped area

For pitch R:12, multiply the horizontal roof plan area by √(1 + (R/12)²). At 6:12 the multiplier is 1.118034; at 12:12 it is 1.414214. Both roof types give the same total area for the same rectangular plan and uniform pitch.

Worked example: a 12 m × 8 m roof footprint

A 400 mm horizontal overhang on all sides gives a 12.8 × 8.8 m roof plan: 112.64 m². At 6:12 pitch the sloped area is 125.94 m². With 10% extra, allow 138.53 m². An example product covering 3.1 m² per bundle needs 45 bundles. Use the unrounded area for ordering, then round up the final bundle count.

Gable and hip lengths

For the example gable, the ridge follows the length input and is 12.8 m. Its two eaves total 25.6 m; the four sloping rake edges total 19.68 m. For an equal-pitch hip roof over the same plan, the ridge is 4 m, the four hips total 26.4 m and eaves total 43.2 m. A square hip plan has a point apex and zero ridge length.

Footprint and overhang

The overhang input is a horizontal plan distance, added twice to both footprint dimensions. On a gable roof this assumes the same projection at eaves and gable ends. For unequal projections, enter the complete roof plan length and width and set overhang to zero. The cross-section spans the width for a gable and the shorter dimension for a hip roof.

Squares, bundle coverage and extra material

One roofing square is exactly 100 ft², or 9.290304 m². Use installed coverage from the package, not a fixed bundles-per-square assumption; see GAF’s explanation of roofing squares. Extra percentage is chosen by you; 10% is an example. Ridge and hip caps, starter strips, underlayment, flashings and fasteners are separate items, not included in the field-shingle bundle count.

Limits of this model

The hip calculation assumes equal pitches on every plane, a rectangular plan and a common eaves level. Intersecting roofs, valleys, dormers, unequal slopes and stepped eaves need a plane-by-plane take-off. This is a geometry and material estimate, not structural sizing or a check that a covering is suitable for the pitch. Length inputs follow mm/inches; coverage and output areas stay in m².