Rafter Calculator
Use our Rafter Calculator to compute rafter lengths, plumb/seat cuts, tails and pitch for gable and skillion roofs
How It Works
The Rafter calculator determines precise rafter measurements based on your roof specifications, accounting for factors like pitch, span, and overhang.
Using trigonometric principles, it calculates the exact rafter length, plumb cuts, seat cuts, and bird's mouth dimensions needed for a structurally sound roof.
Supports both gable and skillion roofs. Skillion mode also allows overhangs (eaves) at the low end, the high end, or both.
Key Features
- Calculate common rafter lengths for gable and skillion roofs
- Determine precise plumb and seat cut angles
- Account for ridge board thickness and wall thickness
- Calculate rafter tail lengths for overhangs
- Support for both imperial and metric measurements
- Skillion option supports overhangs (eaves) at both the high and low ends
How to Use
- Choose the roof type: Gable or Skillion
- Enter the building span
- Specify the roof pitch
- Input ridge board thickness if applicable
- Add seat cut (wall thickness) and overhang measurements
- If Skillion: specify overhangs (eaves) for the low end, the high end, or both
- View complete rafter dimensions and cutting angles
Rafter Calculator
Universal Measurement Support
All calculators support both imperial and metric units
Common Applications
Precision Cutting
Eliminate measurement errors with exact rafter dimensions and angles.
Material Efficiency
Order the right amount of lumber with accurate length calculations.
Time Savings
Skip complex manual calculations and avoid costly mistakes.
Explore Other Features
Oblique Triangle
Use our Oblique Triangle Calculator to solve any triangle with any 3 known values in seconds
Right Angle Triangle
Use our Right Angle Triangle Calculator to simplify right-angle triangle calculations and solve any right triangle quickly and accurately.
Raked Walls
Use our Raked Walls Calculator to calculate stud lengths for raked walls with precision and ease