Roof Pitch Calculator
Convert roof rise and run into pitch, slope percentage, angle, rafter length, roof area, rafter quantity and stock-material cost.
Default project preview
6 in 12
Rafter length
14.53 ft
Slope factor
1.118
Rafter positions
24
Installed rafters
48
Calculator
Build the material order
Your order will appear here
Enter the project details and calculate a rounded material estimate.
Input and output guide
What each value means
The labels and units below are part of this calculator’s visible methodology. Replace every default with measurements or product data from the actual project.
Horizontal rafter run
Enter this project assumption in ft. The current imperial default is 12 ft.
Vertical rise
Enter this project assumption in ft. The current imperial default is 6 ft.
Building length
Enter this project assumption in ft. The current imperial default is 30 ft.
Horizontal overhang
Enter this project assumption in ft. The current imperial default is 1 ft. Minimum: 0.
Rafter spacing
Enter this project assumption in in. The current imperial default is 16 in.
Available stock length
Enter this project assumption in ft. The current imperial default is 16 ft.
Extra rafter allowance
Enter this project assumption in %. The current imperial default is 5 %. Minimum: 0. Maximum: 50.
Price per stock piece
Enter this project assumption in a unitless value. The current imperial default is 25. Minimum: 0.
How to read the outputs
Rafter length
horizontal overhang included. Default preview: 14.53 ft.
Slope factor
plan-to-slope multiplier. Default preview: 1.118.
Rafter positions
16 in centres. Default preview: 24.
Installed rafters
two roof sides. Default preview: 48.
Roof surface
simple gable approximation. Default preview: 872.1 ft².
Stock-piece cost
51 stock pieces. Default preview: $1,275.00.
Methodology
Transparent calculation
BuildMeter converts every input to a consistent internal unit, applies the selected allowance, and rounds products up to whole purchasable units.
Pitch per 12 = rise ÷ run × 12. Angle = arctangent(rise ÷ run). Rafter length = √(run² + rise²) plus the sloped overhang.
Reviewed project guidance
How to use this estimate in a real project
Last reviewed: July 30, 2026
Use this calculator to convert roof rise and run into pitch ratio, slope angle and area multiplier. It supports measurement and material planning but does not determine structural suitability or safe roof access.
Calculation steps
- 1Enter rise and horizontal run in matching units.
- 2Calculate slope as rise ÷ run.
- 3Convert slope to angle with arctangent.
- 4Calculate the area multiplier from the right-triangle hypotenuse.
Worked numerical example
A roof rising 6 inches for every 12 inches of run has a pitch of 6:12, an angle of about 26.6°, and a slope multiplier of approximately 1.118. A 1,000 ft² plan area therefore represents about 1,118 ft² of sloped area before waste.
Purchasing and rounding
The calculator itself does not round products. Apply the multiplier to plan area, then use the relevant roofing, sheathing or underlayment calculator for package rounding.
Interpret the result
A larger multiplier means more sloped surface per unit of plan area. Pitch also affects product suitability and installation methods.
Page-specific assumptions
- Straight uniform roof plane.
- Rise and run describe the same slope.
- No curved or compound geometry.
- Plan area is measured horizontally.
Common mistakes
- Using rafter length as run.
- Mixing degrees and pitch ratio.
- Applying one pitch to multiple roof slopes.
- Using pitch alone to judge walkability.
Primary and technical references
BuildMeter provides planning estimates, not engineering, architectural, electrical, mechanical, plumbing, permit or code approval. Review the methodology and verify final decisions with product documentation and qualified professionals.
BuildMeter Guides
Understand the measurements and assumptions
Use these visible reference guides before changing project inputs or planning allowances.
FAQ
Roof Pitch Calculator questions
What does a 6-in-12 roof pitch mean?+
The roof rises 6 units for every 12 equal units of horizontal run.
Is rafter length the same as roof run?+
No. Rafter length follows the slope and is therefore longer than the horizontal run.
Does this size rafters structurally?+
No. Rafter size depends on span, spacing, loads, species, grade and building code.