Roofing calculator

Enter the building footprint and roof pitch — get the true roof area, squares, shingle bundles or metal area with waste, underlayment rolls and ridge length.

isometricnot to scale

Units

Building length (incl. overhangs)

Building width (incl. overhangs)

Roof shape

Roof pitch

Roof covering

Extra waste % (cuts, complex roofs)

Price per bundle / tile, or per area unit for metal (optional)

Estimates are for planning. Complex roofs with valleys and dormers need more waste — confirm with your roofer.

Material scheduleSheet 01Roofing calculator

Enter the dimensions and press Calculate — the quantities appear here as a printable sheet.

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Frequently asked questions

How do I calculate roof area from the house footprint?

Multiply the footprint (including overhangs) by the pitch factor: at 4/12 the factor is 1.054, at 6/12 it is 1.118, at 9/12 it is 1.25 and at 12/12 it is 1.414. A gable and a hip roof of the same pitch over the same rectangle have almost the same surface area — the shape mainly changes ridge and hip lengths, not the area.

How many bundles of shingles do I need per square?

Three bundles of standard 3-tab or architectural shingles cover one square (100 sq ft). Add 10–15% waste for a simple gable and 15–20% for hips, valleys and dormers, because every cut edge wastes part of a shingle.

How much underlayment do I need?

Cover the full roof area plus 10–15% for the horizontal overlaps (2–4 in) and vertical laps. A typical synthetic roll covers about 4 squares (400 sq ft); #30 felt covers 2 squares per roll.

What roof pitch do shingles and metal need?

Asphalt shingles need at least 2/12 with special underlayment and 4/12 for standard installation. Exposed-fastener metal panels work down to 3/12, standing seam to 1/12. Below that you need a membrane roof, not shingles or panels.