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Roofing calculator
Roof Pitch Calculator
Work out roof pitch from rise and run (or full span): degrees, rise:run ratio, X-in-12, slope percentage and common rafter length. Add roof length to estimate simple gable slope area.
Read the guide: Roof Pitch Calculator.
Free to use. No registration required.
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Read articleFrequently asked questions
How do I calculate roof pitch in degrees?
Pitch angle = arctan(rise ÷ run), converted to degrees. Rise is the vertical height from wall-plate level to the ridge; run is the horizontal distance from the wall plate to the ridge centre.
What is the difference between run and span?
Run is half the roof on a symmetrical gable, wall to ridge. Span is the full eaves-to-eaves width. This calculator can take either: if you enter the full span, run is taken as span ÷ 2.
How is rafter length calculated?
Common rafter length = √(rise² + run²), the hypotenuse of the right triangle formed by rise and run. Add eaves overhang separately if needed; hips, valleys and birdsmouth cuts are not included.
What does pitch ratio or “X in 12” mean?
Pitch ratio is rise:run in simplified form (for example 5:8). “X in 12” is the common US expression of the same slope, how many inches of rise for every 12 inches of run. Slope percentage is (rise ÷ run) × 100.
How do I work out roof slope area?
Enter the roof length along the ridge. One slope area ≈ rafter length × roof length. For a simple gable with two equal slopes, multiply by two. Hips, dormers and valleys need a more detailed take-off.
Is a steeper pitch always better?
Not necessarily. Steeper pitches shed water and snow more readily but use more material and change the look and attic volume. Follow the covering manufacturer's minimum pitch and the structural design for your building.