Roof Area and Pitch Calculator

Measure the footprint of the building at ground level, wall to wall. The calculator adds the eaves for you.

Roof formPick the shape that matches most of the roof

Hip Gable Skillion Flat

FootprintLength and width in metres, plus the eave overhang in millimetres

Length, m

Width, m

Eave, mm

Australian roofs are specified in degrees, not in twelfths. A tiled roof is usually 17.5 to 25 degrees, sheet metal can go much lower.

Common pitchesTap one, or type any angle below

Pitch in degreesAnything from 0 to 60 degrees

The roof area drives the paint. Change the spread rate if your tin states a different figure.

CoatsMost roof membrane systems are two coats over a primer

Spread rateSquare metres per litre per coat. Roof membrane defaults to 5.

Roof surface area

Enter your footprint

Plan area first, then the slope factor for your pitch.

Your working will appear here.

The same pitch in every unit a builder, plumber or plan might use.

What this calculator assumes

Plan area is the footprint plus the eave overhang on all four sides, so plan area equals (length plus twice the overhang) multiplied by (width plus twice the overhang).
Roof area is plan area multiplied by the slope factor, where the slope factor is 1 divided by the cosine of the pitch.
Hip and gable roofs are treated as a single pitch across the whole plan. A flat roof uses a slope factor of 1.
Gable ends are wall area, not roof area. Each end is the width squared multiplied by the tangent of the pitch, divided by 4. They are reported separately.
Litres use a roof membrane spread rate of 5 square metres per litre per coat, over a sound and primed surface. Cans round up to the Australian ladder of 1, 2, 4, 10, 15 and 20 litres.
Dormers, penetrations, valleys and complex multi pitch roofs add area. Treat the result as a close estimate, not a set out.

Roof surface area

Enter your footprint

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