Roof Pitch Calculator
Enter any rise and matching horizontal run in the same units to normalize the roof slope into the common rise-per-12 format.
What does the roof pitch calculator calculate?
Roof pitch is rise divided by horizontal run. This calculator normalizes that ratio to inches of rise per 12 inches of run, converts it to degrees and percent grade, and computes the slope factor used to turn horizontal plan area into sloped roof area.
Roof pitch conversion formulas
All outputs begin with the dimensionless rise-to-horizontal-run ratio. Scaling gives x:12 pitch, trigonometry gives angle, and the hypotenuse relationship gives the surface multiplier.
How to measure for an accurate estimate
- Measure rise vertically and run horizontally with both values in the same unit.
- Do not use rafter or roof-surface length as run; run is the level horizontal projection.
- Measure from plans, an accessible attic framing member, or a digital level without entering a hazardous roof.
- Check multiple locations when an existing roof may sag, settle, or contain sections with different pitches.
Six inches of rise over twelve inches
A roof rises 6 inches across a level horizontal run of 12 inches.
The pitch is 6:12, the slope angle is 26.57 degrees, the grade is 50%, and the roof-area slope factor is 1.1180.Before you purchase material
- Confirm the roof covering’s minimum and maximum permitted slope before selecting a system.
- Use the slope factor only on horizontal plan areas that share the measured pitch.
- Do not size rafters, trusses, beams, drainage, or fasteners from pitch alone.
- Give suppliers the normalized x:12 pitch plus drawings showing hips, valleys, dormers, and roof dimensions.
Common questions
What does a 6:12 roof pitch mean?
A 6:12 pitch rises 6 vertical inches for every 12 horizontal inches of run. It corresponds to a 50% grade and an angle of about 26.57 degrees. The notation describes slope, not rafter size or roof strength.
Is roof pitch the same as roof angle?
They describe the same slope in different formats. Pitch uses a rise-to-run ratio, usually normalized to 12 inches of run in U.S. construction. Angle expresses that ratio in degrees using the arctangent mathematical function.
What is a roof slope factor?
The slope factor is sloped length divided by horizontal run. Multiplying a matching horizontal plan area by this factor estimates surface area for a uniform roof plane. It does not add overhangs or material waste automatically.
Can roof pitch determine whether shingles are allowed?
Pitch is one criterion, but the complete roof system, underlayment, climate, manufacturer listing, and building code also matter. Low slopes may require special details or another covering. Confirm the exact product instructions and local approval.
Sources and reference standards
- FEMA — Protect Your Property From High WindsFederal guidance on roof-covering attachment and wind-resistant construction.