LoadingLoadingLoadingLoadingEnter the building footprint and the pitch, pick the roof shape, and get the true sloped area — the figure you actually order tiles, slates, membrane and battens against.
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Measure the footprint to the outside of the eaves overhang, not the wall line. Hip and pyramid roofs have the same sloped area as a gable at the same pitch — they just lose more tiles in the cutting, which is why the suggested waste changes with the shape.
Plan area
60,0 m²
Slope multiplier
× 1,221
Plan area × this multiplier = sloped area. It's 1 ÷ cos(pitch).
Roof surface area
73,2 m²
With 5% waste
76,9 m²
Suggested allowance for cutting at verges, hips and valleys — order materials against this figure.
Estimates only. Complex roofs with dormers, valleys or mixed pitches should be measured section by section and added up. Always confirm quantities before ordering.
The most common estimating mistake on a re-roof is ordering against the footprint. A 35° pitch adds 22% to the area; a 45° pitch adds 41%. Order against the plan and you're a pallet short by the second day.
The conversion is pure geometry: divide the plan area by the cosine of the pitch. This calculator does that and suggests a shape-based waste allowance, because a hipped roof at the same pitch covers the same area but wastes more tiles in the cutting.
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