Roof Area Calculator

How the calculator works

The calculation starts from the roof base area, which is simply length multiplied by width. Because the roof slopes, the actual surface of the roof is always larger than the footprint: the steeper the pitch, the more material the same base requires.

For example, a house measuring 10 by 8 metres has an 80 m² footprint. A shallow pitch increases the area only slightly, while a steep gable roof raises the slope area noticeably.

What you enter and what you get

Enter the base length, base width and roof pitch in degrees. The tool reports the base area, the roof slope area, and a material figure with a 10% waste margin added for cuts and overlaps.

The waste margin gives you a number you can hand straight to a supplier when ordering.

Who it is for

It is handy for anyone building a house, replacing a roof or budgeting a renovation. With realistic square-metre figures you can request accurate quotes before buying any material.

Good to know

The result is an estimate for a simple gable roof. If the roof has dormers, valleys or other complex details, add extra waste on top of the 10%, because such roofs involve more cutting and fitting.