Construction & Materials · Verified formula
Roof Pitch Calculator
Convert rise and run into roof pitch, slope percentage, angle and rafter length.
Formula verified
3+ known-answer test cases
Last verified August 2026
Result
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How to use the Roof Pitch Calculator
- Measure rise (vertical) and run (horizontal) over the same reference length — 12 inches of run is standard.
- Enter both values in the same units.
- Optionally enter the full roof span to estimate total rafter length.
- Select Calculate to see pitch, slope %, angle and rafter length.
Formula
Pitch, angle and rafter length
Pitch = rise ÷ run Angle = arctan(rise ÷ run) Rafter length = √(rise² + run²)
Worked example
Verified example
QA passed
Rise: 6 in, Run: 12 in Pitch = 6 ÷ 12 = 0.5 → expressed as 6:12 Slope = 0.5 × 100 = 50% Angle = arctan(0.5) ≈ 26.565° Result: 6:12 pitch, 50% slope, ≈26.565° angle
Why this matters: Pitch determines material choice — some roofing materials have a minimum pitch requirement — and it drives rafter length for framing, so an error here compounds into the material order.
Common mistakes
- Measuring rise and run over inconsistent reference lengths instead of a standard 12 in run.
- Confusing pitch (a ratio, like 6:12) with angle (in degrees) — they describe the same slope but aren't the same number.
- Using the rafter-length-per-run figure for the full roof span instead of just the sloped rafter section.
Frequently asked questions
What does a 6:12 roof pitch mean?
For every 12 inches of horizontal run, the roof rises 6 inches. That works out to a 26.6° angle and a 50% slope.
How do I measure my existing roof pitch?
Hold a level horizontally against the roof surface, measure 12 inches out from the high end, then measure the vertical distance down to the roof at that point.
How does pitch affect material needs?
Steeper pitches increase the actual roof surface area relative to the footprint, which increases the shingles, underlayment and rafter length required.
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