Roof Rafter Calculator
Calculate simple-gable rafter length, rise, rafter positions, stock pieces, roof surface area and preliminary lumber cost.
Default project preview
17.89 ft
Vertical rise
7.5 ft
Rafter positions
31
Installed rafters
62
Stock pieces
66
Calculator
Build the material order
Your order will appear here
Enter the project details and calculate a rounded material estimate.
Methodology
Transparent calculation
BuildMeter converts every input to a consistent internal unit, applies the selected allowance, and rounds products up to whole purchasable units.
Run = building width ÷ 2. Rise = run × pitch ÷ 12. Rafter length = √(run² + rise²) plus the sloped overhang. Positions follow entered spacing.
FAQ
Roof Rafter Calculator questions
Does rafter length include the overhang?+
Yes. The horizontal overhang is converted to sloped length using the pitch factor.
Is rafter quantity twice the number of positions?+
For a simple gable roof, each position has one rafter on each roof side.
Does this select rafter size?+
No. Member size depends on span, species, grade, spacing, loads and code.