Rafter Length Calculator
Calculate rafter length, roof truss dimensions, and estimate construction costs for your roofing project
Calculate Rafter Dimensions
Horizontal distance from wall to ridge center
Vertical height from wall top to ridge
Rafter Length Results
Formula used: Rafter Length = √(Rise² + Run²)
Calculation: √(0.00² + 0.00²) = 0.00 feet
Example Calculation
Residential Roof Example
Building Width: 24 feet
Run: 12 feet (half the span)
Roof Pitch: 6:12 (6 inches rise per 12 inches run)
Rise: 12 ft × (6/12) = 6 feet
Calculation
Rafter Length = √(Rise² + Run²)
Rafter Length = √(6² + 12²)
Rafter Length = √(36 + 144)
Rafter Length = √180
Rafter Length = 13.42 feet
Roof Components
Rafter
Structural beam that supports the roof deck
Truss
Pre-fabricated framework of rafters and supports
Pitch
Angle or slope of the roof surface
Span
Total width of the building (run × 2)
Common Roof Pitches
Construction Tips
Add 6-12 inches to rafter length for overhang
Consider birdsmouth cuts for wall bearing
Check local building codes for rafter sizing
Account for ridge beam thickness in calculations
Use proper lumber grade for structural loads
Understanding Rafter Length Calculations
What is Rafter Length?
Rafter length is the distance from the top of the wall to the ridge of the roof, measured along the slope. It's essential for determining the amount of lumber needed for roof construction and ensuring proper structural support.
Why Accurate Calculation Matters
- •Ensures structural integrity and safety
- •Prevents material waste and cost overruns
- •Meets building code requirements
- •Enables proper roof drainage and weather protection
Pythagorean Theorem Application
Rafter Length = √(Rise² + Run²)
The same formula used for right triangle hypotenuse
- Rise: Vertical height from wall to ridge
- Run: Horizontal distance from wall to ridge center
- Span: Total building width (run × 2)
- Pitch: Rise/run ratio, often expressed as X:12
Safety Note: Always consult with a structural engineer for load-bearing calculations and local building codes for residential and commercial construction.