Centered-ridge assumption
The calculator uses half the building width, adjusted for the entered ridge thickness.
Free contractor tool
Rafter & Roof Pitch Calculator
Get the common-rafter triangle from building width, pitch and overhang without reaching for a framing table.
Pitch /12Common rafterRoof angle
Common-rafter geometry
Enter the full building width, roof pitch and eave overhang. The tool assumes a centered ridge.
Geometry only. Rafter size, span, species, birdsmouth limits, connectors, ridge design, loads and local code still require structural/permit verification.
Roof triangle
The sketch shows the calculated half-span and pitch geometry.
Pitch becomes an angle
A 6/12 pitch rises six inches for every 12 inches of horizontal run. The roof angle is arctan(rise/run).
Structural sizing is separate
This is geometry, not a span table. Verify lumber size, species, loads, connections and birdsmouth limits separately.