Roof Pitch Angle
Calculator

Roof pitch is usually expressed as a ratio of vertical rise to horizontal run over a 12-inch span — a '6/12 pitch' means the roof rises 6 inches for every 12 inches of horizontal distance. It's a slope measurement, not a direct angle.

It takes the arctangent of rise divided by run (angle = arctan(rise/run)) — for a 6/12 pitch, that's arctan(6/12) = arctan(0.5) ≈ 26.57 degrees. This trigonometric relationship is what links the construction-trade pitch notation to a standard angle.

The rise/run notation maps directly onto a carpenter's square and speed square, both marked in inches, making it easy to measure and mark angles on site without any trigonometry — degrees are more familiar in general math but less practical for on-site tools.

Roofs under about 3/12 (roughly 14 degrees) are generally considered low-slope and often need different roofing materials (like membrane roofing) than steeper roofs; roofs steeper than about 9/12 (about 37 degrees) are considered steep and require additional safety precautions for installation.

Yes — as pitch increases, the actual roof surface area for a given building footprint increases too, since the sloped surface is always longer than its horizontal projection. This is exactly why the pitch angle is a required input for the related roof-area-by-pitch calculation.