How do you convert roof pitch?
Pitch comes from the rise and the horizontal run. The angle is arctan(rise ÷ run), the slope in percent is rise ÷ run × 100, and the ratio is the rise per 1 metre of run. The rafter length is √(run² + rise²) by Pythagoras. Many roof coverings have a minimum pitch — always check the manufacturer’s specification.
Frequently asked questions
How many degrees is a 100% slope?
A 100% slope means equal rise and run, so 45°. 50% is about 26.6°.
Percent vs degrees?
Percent is rise/run × 100; degrees is the actual angle. They are not linear: 100% = 45°, but 200% ≈ 63°.
When is a roof "flat"?
A roof up to about 5° (roughly 9%) is usually classed as a flat roof; above that it is a pitched roof.
How long are my rafters?
The calculator gives the roof-plane length (√(run² + rise²)). Add overhang and junctions for the real rafter length.