Roof Pitch Calculator
Work out a roof's pitch, angle and rafter length from its rise and run.
Reading a roof's slope
A roof's pitch is its steepness, expressed as a ratio of rise to run or as an angle, and it determines the rafter length, the materials suitable, and how the roof sheds water. This works out the pitch, the angle and the rafter length from the rise and run, the essential geometry of roofing.
Enter the rise and run to see the pitch, angle and rafter length.
Why pitch matters beyond looks
Pitch is not just an aesthetic choice. A steeper roof sheds rain and snow faster and gives more attic space, but uses more material and is harder to work on; a shallow roof is cheaper and easier but can struggle with heavy snow and standing water. Crucially, different roofing materials have minimum pitches below which they leak, so the pitch constrains what you can cover the roof with. The rafter length comes straight from the pitch geometry, using the same right-angle maths as any slope.
Frequently asked questions
Why does roof pitch matter?
It affects how well the roof sheds water and snow, the attic space, the material cost, and which roofing materials can be used without leaking.
How is rafter length found from pitch?
From the right-angle geometry of the rise and run — the rafter is the sloping side of the triangle the roof forms.
Is anything uploaded?
No. The calculation happens in your browser.