Roof Pitch Calculator
Pitch, angle, slope & rafter length
Enter rise and run
Height from wall top to ridge
Half the building span
Your results
Enter your project details to see results.
Formula & explanation
Roof pitch is expressed as inches of rise per 12 inches of run. The degree angle comes from the arctangent of the slope. The rafter length is the hypotenuse of the rise-run triangle — the actual board from wall plate to ridge.
Example calculation
Rise 6 ft, run 12 ft:
Pitch = 6÷12 × 12 = 6/12. Angle = arctan(0.5) = 26.6°. Slope = 50%. Rafter = √(36+144) = 13.42 ft.
Buying & project-planning tips
- Low-slope roofs (under 2/12) need special membrane roofing — shingles aren't suitable.
- Rafter length here is theoretical — add overhang (eave) length for the actual board size.
- Use the 6/12 threshold: steeper roofs typically need safety harnesses and may cost more to install.
- Local snow load may require a steeper pitch or additional structural reinforcement.
Frequently asked questions
What is a standard roof pitch?+
Most homes use between 4/12 and 9/12. Below 3/12 is considered low-slope and needs membrane roofing; above 10/12 is steep-slope.
How do I measure roof pitch from the ground?+
Measure one foot horizontally along the gable wall, then measure vertically to the roof surface — that's the rise per 12 inches of run.
What pitch is walkable?+
Roofs up to about 7/12 are generally walkable in dry conditions. Steeper roofs need fall protection and professional installation.
Does pitch affect roofing material choice?+
Yes — shingles typically need 2/12 or steeper. Low-slope roofs (under 2/12) require rolled membrane or standing-seam metal.