Roof Truss Calculator
Calculate roof truss count, rafter length, and construction costs for your roofing project
Calculate Roof Truss Requirements
Length of the building or roof ridge
Distance between truss centers (typical: 16", 24")
Truss Count Results
Formula: Truss Count = ((Roof Length × 12) / Spacing) + 1
Calculation: ((0 × 12) / 24) + 1 = 0 trusses
Note: Formula assumes roof length in feet and spacing in inches
Example Calculations
Truss Count Example
Roof Length: 40 feet
On-Center Spacing: 24 inches
Calculation: ((40 × 12) / 24) + 1 = (480 / 24) + 1 = 20 + 1
Result: 21 trusses needed
Rafter Length Example
Run: 12 feet
Rise: 6 feet (6:12 pitch)
Calculation: √(6² + 12²) = √(36 + 144) = √180
Result: 13.42 feet rafter length
Common Truss Types
Fink Truss
Most economical, lightweight, quick to build
Best for: Simple gable roofs
King Post Truss
Traditional design, good for smaller spans
Best for: 8-25 foot spans
Attic Truss
Provides usable attic space
Best for: Storage or living space
Scissor Truss
Creates vaulted ceiling effect
Best for: Cathedral ceilings
Standard Truss Spacing
Note: Always consult local building codes and structural engineers for your specific requirements.
Installation Tips
Order one extra truss for safety margin
Check delivery access and crane requirements
Ensure proper bearing wall support
Use temporary bracing during installation
Follow manufacturer's installation guide
Consider professional installation for safety
Understanding Roof Truss Calculations
What is On-Center Spacing?
On-center (OC) spacing refers to the distance measured from the center of one truss to the center of the next truss. This measurement is crucial for structural integrity and material calculations in roof construction.
Why Accurate Calculation Matters
- •Ensures structural safety and building code compliance
- •Prevents material waste and cost overruns
- •Enables proper load distribution
- •Facilitates accurate project planning and scheduling
Calculation Formulas
Truss Count: ((Length × 12) / Spacing) + 1
Rafter Length: √(Rise² + Run²)
Always round up truss count to nearest whole number
- Length: Building length in feet
- Spacing: On-center distance in inches
- Rise: Vertical height to peak
- Run: Horizontal distance to center
Safety Note: Always consult with structural engineers and follow local building codes. Truss design must account for load requirements, wind, and snow loads.