Roof Pitch Calculator

Roof pitch is the steepness of a roof, and getting it right matters whether you are framing a new roof, building a pergola or lean-to, choosing roofing material, or checking a pitch meets a manufacturer's minimum fall for proper drainage. This calculator works out the pitch three ways from two simple measurements. Enter the rise, the vertical height the roof climbs, and the run, the horizontal distance it covers, in the same units such as metres. The calculator instantly returns the pitch angle in degrees, the pitch ratio expressed as a rise in 12 (the format tradies and roofing suppliers use, such as 6 in 12), and the rafter length, the actual sloping distance along the roof line from Pythagoras' theorem. The maths behind it is straightforward trigonometry: the angle is the inverse tangent of rise divided by run, the ratio scales that same relationship to a run of 12, and the rafter length is the square root of the rise squared plus the run squared. A 3 metre rise over a 6 metre run, for example, gives an angle of about 26.6 degrees, a 6 in 12 pitch, and a rafter length of roughly 6.7 metres. Use the results to compare against a roofing product's minimum pitch, order the right length of rafters or trusses, or simply understand how steep a roof design really is before committing to it.

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