Home & Construction
Roof Pitch Calculator
Calculate slope length, pitch angle, pitch per 12, two-plane roof area, area factor, and waste-adjusted order area. The custom roof section and plan connect the numeric results with the physical surfaces being measured.
Estimated two-slope roof area-
Roof angle (degrees)-
Pitch rise per 12 units run-
Rafter length before overhang-
Roofing order area including waste-
Slope-area factor-
Decision view
Roof section and surface takeoff
Roof section and surface takeoffRun, rise, rafter line, two roof planes, overhang, and waste-adjusted order area are connected geometrically.
Exact scenario comparisonVertical rise (m) changes while all other entered assumptions remain constant.
| Vertical rise (m) | Estimated two-slope roof area | Roof angle (degrees) | Pitch rise per 12 units run | Rafter length before overhang | Roofing order area including waste | Slope-area factor |
|---|
How to use Roof Pitch Calculator
- Measure horizontal run from ridge projection to eave line rather than along the roof surface.
- Enter vertical rise over that same run and the roof length parallel to the ridge.
- Add overhang and waste deliberately, then reconcile valleys, hips, dormers, penetrations, and product coverage separately.
Calculator guide
Understanding Roof Pitch Calculator
Roof pitch is right-triangle geometry. Horizontal run and vertical rise determine slope length, angle, rise per 12 units of run, and the area multiplier that converts a horizontal plan into sloped roof surface.
Calculation method
How the calculation works
Use rise and horizontal run to calculate roof angle, pitch ratio, slope length, and the two-slope surface area including horizontal overhang. Use the Pythagorean theorem for one slope, arctangent for angle, divide rise by run for pitch, multiply two slopes by building length, then add the entered waste allowance.
Takeoff boundary
Know what the simple gable model includes
The arithmetic is exact for the entered geometry but the building may contain more surfaces.
Worked situations
Practical examples
- A 6 m run and 3 m rise produce a 6.708 m slope length.
- The same geometry is a 6-in-12 pitch and an angle of about 26.565 degrees.
- For a simple two-plane roof, two slope rectangles are multiplied by building length before waste is added.
Better inputs
Useful tips
- Use one consistent length unit across run, rise, length, and overhang.
- Measure each distinct roof plane when geometry is not a simple symmetric gable.
- Convert area to bundles, sheets, rolls, or panels using manufacturer net coverage.
Before relying on the result
Limitations and common mistakes
- The model represents a symmetric two-plane roof and does not subtract openings.
- Hips, valleys, dormers, curved roofs, flashing, ridge caps, underlayment, fastening, laps, and code requirements are excluded.
- Field measurements and safe access should be performed by qualified personnel.
Reference
Key terms
- Run
- Horizontal distance from ridge projection to the eave reference.
- Rise
- Vertical change over the entered run.
- Slope length
- Diagonal rafter-line distance over one roof plane.
- Area factor
- Slope length divided by horizontal run.
Important note
Calculated from the entered measurements and stated coverage or quantity rules. Confirm field dimensions, waste, product requirements, structural conditions, and local codes before purchasing or building.
Frequently asked questions
Is run the same as rafter length?
No. Run is horizontal; slope length follows the roof surface.
What does 6-in-12 mean?
The roof rises 6 units for every 12 horizontal units.
Why is roof area larger than plan area?
Sloped surface length exceeds its horizontal projection.
Can this price a complex roof?
Use it for individual simple planes, then add geometry and product-specific requirements separately.