Gable roof calculator — common rafters, ridge height and roof geometry.
A symmetrical gable roof is the clearest place to understand the relationship between building span, roof pitch, ridge height, common rafters and overhang.
Basic gable roof geometry
With a centered ridge and equal roof pitches:
run = span ÷ 2
rise = run × pitch ratio
rafter length = √(run² + rise²)
These values describe the theoretical roof triangle before workshop details such as ridge thickness, support notches and rafter tails are applied.
Ridge height
The ridge height is the vertical rise from the chosen wall-plate reference to the ridge line. A steeper roof increases both the ridge height and the common-rafter length.
Rafter spacing
After the geometry is defined, the building length and target spacing determine how many rafter positions are needed. The final arrangement should be explicit rather than relying only on a nominal spacing value, especially near end walls and openings.
Openings in a gable roof
Roof windows and chimneys can interrupt common rafters. A complete model should show which rafters are cut, where the real segments end and which trimming elements frame the opening.
What Krokwio adds
Instead of calculating only the roof triangle, Krokwio uses the gable-roof geometry to generate and organize actual framing elements. You can review the roof in 2D and 3D, open element cards, inspect notches and prepare the project for workshop documentation.
Related: Rafter Calculator, Ridge Height Calculator, Roof Framing Cutting List.
Turn roof geometry into workshop-ready information.
Use one project for geometry, 2D/3D views, element cards, cutting data, PDF documentation and QR identification.