How to work out roof pitch
Back to calculator ↑The roof angle formula
Angle = arctan(rise ÷ run). The run is the horizontal distance from the eave to the point below the ridge, not the full roof width. For example, a 1.5 m rise over a 4 m run is about 20.6 degrees.
Rafter length
Rafter length = √(rise² + run²). The same example gives about 4.27 m. Add any overhang measured along the slope.
Limits
Minimum pitch depends on the roofing product, so check the manufacturer's guide. Have structural design checked by a qualified person.
Common questions
What is the run?
It is the horizontal distance from the eave to the point below the ridge. On a symmetrical gable, it is half the width.
What angle is a 100% slope?
45 degrees, because the rise equals the run.