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HeizerDesk Roof Pitch Calculator
Give it the rise and the run and it returns the pitch in every form you might be asked for — the x/12 ratio, the angle in degrees, the slope factor that converts footprint to actual roof area, and the rafter length.
Your numbers
Result
Pitch
6
in 12
- Angle
- 26.57°
- Slope factorMultiply footprint by this for roof area
- 1.118
- Grade
- 50%
- Rafter lengthHalf span along the slope, plus overhang
- 17.77ft
- Ridge above the plate
- 7.5ft
How this is calculated
- Pitch ratio = rise ÷ run × 12, written as x/12.
- Angle in degrees = arctangent(rise ÷ run).
- Slope factor = √(rise² + run²) ÷ run. A 6/12 roof gives 1.118.
- Rafter length = (span ÷ 2) × slope factor + overhang.
- Ridge height above the wall plate = (span ÷ 2) × (rise ÷ run).
Before you order
- Slope factor is the number that matters for ordering: footprint × slope factor = actual roof surface. Skip it and you under-order every time.
- Below 2/12 is low slope and most shingles are not rated for it — that is membrane territory, and installing shingles there voids the warranty.
- Anything over about 6/12 usually means staging or roof jacks, which changes the labour line more than the material line.
- Rafter length here is the theoretical line length. Subtract half the ridge board thickness and cut your birdsmouth from the measured seat.