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Rafter Length Calculator — result sheet
Estimate sloping rafter length, roof angle, and total material length from horizontal run, rise, overhang, and count.
Inputs used
Results
Visual chart
Breakdown
Calculation steps
Returned data table
Formula and methodology
Formula: Slope length = √(run² + rise²) + overhang; roof angle = atan2(rise, run); total order length = slope length × count × (1 + waste/100).
The right-triangle calculation reports the sloping member separately from the overhang and material allowance.
This result follows the calculator's declared inputs, precision, validation boundaries, and model limits.
Input contract
- Horizontal run — m; minimum 1.0E-6; maximum 1000000
- Rise — m; minimum 0; maximum 1000000
- Overhang allowance — m; minimum 0; maximum 1000000
- Rafter count — minimum 1; maximum 1000000
- Waste allowance — %; minimum 0; maximum 1000
Worked example
| Input | Value |
|---|---|
| Horizontal run | 3 |
| Rise | 1 |
| Overhang allowance | 0.3 |
| Rafter count | 20 |
| Waste allowance | 10 |
Rafter length = 3.462 m, roof angle ≈ 18.435°, and order length ≈ 76.17 m.
Assumptions and limits
- Run and rise describe one straight roof slope and use the same unit.
- Overhang is measured along the slope and the count includes all equal rafters.
- Birdsmouth cuts, ridge details, support reactions, snow or wind loads, deflection, bracing, and code design are not modeled.
Calculator note
Source and methodology
Use the official WorldCalculate methodology policy for the source, formula, precision, and boundary standards behind this calculator.
Planning estimate, not financial, medical, legal, or professional advice. © WorldCalculate — reuse with attribution. Built and curated by Hassan ALRowaie.
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