Calculate roof rafter length from span, run, pitch, overhang, ridge adjustment, and birdsmouth allowance. Use this rafter length calculator for gable roofs, shed roofs, lean-to roofs, roof framing takeoffs, rafter cuts, roof area estimates, and preliminary planning.
Roof run:
The calculator finds the horizontal run from building width or a known run, depending on the selected mode.
Pitch factor:
The calculator converts roof pitch into a slope factor, then multiplies that factor by the adjusted run.
Overhang and ridge:
The calculator can add overhang and tail allowance and subtract half the ridge thickness when selected.
Material check:
The calculator compares the final rafter length with the available board length and estimates roof area from rafter spacing and roof length.
A rafter length calculator helps estimate the sloped length of a roof rafter before cutting lumber or planning roof framing.
It can help compare roof run, rise, pitch angle, slope factor, overhang length, ridge adjustment, roof area, rafter count, and board length.
Your result shows estimated roof run, roof rise, slope factor, pitch angle, rafter length without overhang, final rafter length with allowances, board length check, roof area, and estimated rafter count. These are planning estimates only.
Find the roof run, apply the roof pitch slope factor, then add overhang or tail allowances if needed. For a gable roof, the run is usually half the building width.
Roof run is the horizontal distance from the outside wall or bearing point to the ridge or high point of the roof.
It can. This calculator shows the base rafter length and the final rafter length after overhang, ridge adjustment, tail allowance, and birdsmouth allowance.
No. Actual rafter cuts depend on ridge thickness, birdsmouth layout, fascia detail, overhang detail, roof framing style, lumber sizes, and local building requirements.