Measure first
Measure finished dimensions, actual stock, openings, and site constraints before ordering material.
Roof planning
Rafter Length Calculator
Estimate the diagonal length of a common rafter from its horizontal run, rise, and overhang. The output also shows pitch and angle for early material planning.
How the estimate works
Use the number as a planning starting point.
The length is the hypotenuse of the roof triangle: square root of rise squared plus the adjusted horizontal run squared.
Check the result
This is geometry only. Birdsmouth, ridge deduction, heel height, structural loading, material grade, and connection details must be designed for the actual building.
Plan the next step
Use the related calculators below to turn a first estimate into a material list, layout, or a more detailed project plan.
FAQ
Common Rafter Length Calculator questions
Does rafter length include a birdsmouth cut?
No. The diagonal estimate is not a cut list. Layout deductions and bearing details must be set from the actual design.
Can I use this for trusses?
No. Trusses are engineered assemblies and should follow approved plans.
Related tools
Keep the project moving.
Roof Pitch Calculator
Free roof pitch calculator. Convert rise and run into roof pitch, angle, slope percentage, pitch multiplier, and an approximate common-rafter length.
Open Roof Pitch CalculatorRoof Shingle Calculator
Free roof shingle calculator. Estimate roof area, roofing squares, shingle bundles, and waste allowance from building size and roof pitch.
Open Roof Shingle CalculatorStair Angle Calculator
Free stair angle calculator. Convert stair rise and run into degrees, slope percentage, pitch ratio, and approximate stringer length.
Open Stair Angle CalculatorPlanning disclaimer: WoodCutTool results are estimates. Verify measurements, product instructions, material condition, local requirements, and safety practices before buying, cutting, or building.