Home & Construction
Rafter Length Calculator - Calculate rafter length and cuts for roof framing
Calculate rafter length and cuts for roof framing
Formulas and edge cases are reviewed against authoritative references before publication. For methodology, editorial standards, or corrections, use the links below.
Frequently asked questions
How is pitch expressed?
As rise over run, e.g., 6/12 means 6 inches of rise per 12 inches of horizontal run.
What about the ridge board?
Subtract half the ridge board thickness from the run for accurate rafter length.
How to mark cuts?
Use a framing square with pitch numbers to mark plumb and seat cuts accurately.
Related tools
About this tool
Inputs
- Roof Span
- Roof Pitch
- Overhang Length
- Ridge Board Thickness
- e.g., 6/12
Results
- Rafter Length
- Run Length
- Rise Height
- Plumb Cut Angle
- Seat Cut Angle
Whether you are planning ahead or double-checking existing numbers, the Rafter Length Calculator delivers instant answers from the figures you provide. Start by filling in roof span, roof pitch, overhang length, ridge board thickness and e.g., 6/12. Based on these values, the tool computes rafter length, run length, rise height and other key metrics. People frequently need to calculate rafter length and cuts for roof framing but lack a quick way to do it — this tool fills that gap.
Measure twice, order once — re-measuring saves far more than the few minutes it costs. Material waste factors (typically 5-15%) should be added on top of the theoretical amount. Use a framing square with pitch numbers to mark plumb and seat cuts accurately. Brick count = wall area ÷ face area of one brick, adjusted for mortar joint thickness. Results are rounded for display; the underlying computation retains full precision.