Inputs
Formulas Used
Definitions. Run is half the building span (horizontal). Rise is vertical height from plate to ridge. The angle is measured from horizontal.
- Given angle θ (degrees):
height = run × tan(θ) - Given slope r per 12:
height = run × (r / 12), angleθ = arctan(r/12) - Given ratio a:b:
height = run × (a / b), angleθ = arctan(a/b) - Given percent p:
height = run × (p / 100), angleθ = arctan(p/100) - Rafter length:
rafter = √(run² + height²) - Total building height (optional):
total = foundation + wallHeight + height
Assumes simple symmetrical gable geometry without ridge thickness. For complex roofs, treat the governing run to the ridge similarly.
Results
| Metric | Value |
|---|---|
| Units | - |
| Run | - |
| Ridge height above plate | - |
| Rafter length | - |
| Pitch angle (°) | - |
| Slope (rise per 12) | - |
| Rise:Run ratio | - |
| Percent grade (%) | - |
| Total building height (optional) | - |
How to Use
- Select Units: feet or meters.
- Enter either Run or Span. Leave one blank.
- Choose an Input mode and provide its value(s).
- Optionally add Wall height and Foundation to compute the total height.
- Click Calculate. Review results and export as CSV or PDF.
Example Data Table
| Example | Span | Run | Input Mode | Value | Ridge Height | Angle (°) |
|---|
FAQs
It returns ridge height, rafter length, angle, slope as rise‑per‑twelve, ratio, percent, and optional total building height above grade.
Yes. Span is the full building width. The calculator uses half of that (run) for trigonometric computations.
Results use exact math with your inputs. Field conditions, material thicknesses, and framing details may require allowances not modeled here.
No. Choose a unit system and enter all linear dimensions consistently in those units for correct results.
Select “Slope (rise per 12)” and enter 7. The tool converts that to angle, percent, and height automatically.
No. Ridge height depends on structural run to the ridge, not eave overhang. Overhang affects rafter length outside the wall line.
Yes. Enter wall height and foundation above grade. The calculator adds those to ridge height for a total.
Reference: Common Slopes and Angles
| Slope (rise/12) | Angle (°) | Percent (%) | Rise:Run ratio | Rise per 1 unit run |
|---|
Reference: Ridge Height by Span & Slope
Computed for common spans and slopes. Values update with selected units.