Roof Pitch Calculator
Roof pitch expresses the vertical rise relative to horizontal run and can be displayed as rise per 12 units, a percentage and an angle.
How to use this calculator
- Enter the rise and horizontal run using the same units. You will see pitch, grade, angle and rafter length.
- Check the labels and units before using a result outside this page.
- Change one input at a time if you want to compare scenarios.
Formula and method
Pitch per 12 = 12 × rise/run; grade = 100 × rise/run; angle = arctan(rise/run)
- Pitch per 12 = 12 × rise/run; grade = 100 × rise/run; angle = arctan(rise/run)
- Enter horizontal run rather than sloping rafter length. This estimate does not replace structural design or local code requirements.
Worked examples
Worked example
Rise 4 and run 12 in the same unit.
Pitch is 4:12, slope is 33.33%, and angle is about 18.43°.
Pitch is 4:12, slope is 33.33%, and angle is about 18.43°.
Understanding the result
Roof pitch expresses the vertical rise relative to horizontal run and can be displayed as rise per 12 units, a percentage and an angle.
Enter horizontal run rather than sloping rafter length. This estimate does not replace structural design or local code requirements.
Important notes
Enter horizontal run rather than sloping rafter length. This estimate does not replace structural design or local code requirements.
Displayed outputs are rounded for readability; preserve full precision when continuing a calculation.
Frequently asked questions
What does this roof pitch calculator show?
Roof pitch expresses the vertical rise relative to horizontal run and can be displayed as rise per 12 units, a percentage and an angle.
Which inputs should I check first?
Enter the rise and horizontal run using the same units. You will see pitch, grade, angle and rafter length.
Can the result be used as a final professional specification?
Enter horizontal run rather than sloping rafter length. This estimate does not replace structural design or local code requirements.
Related calculators
- Drainage Slope Calculator — Calculate fall per metre, slope grade, and horizontal-to-vertical ratio for drainage runs.
- Roofing Calculator — Estimate roof surface area from a rectangular plan footprint and a selected pitch factor.
- Board Foot Calculator — Calculate board feet from lumber thickness, width, and length.
- Concrete Calculator — Estimate concrete volume for a rectangular slab or pad from length, width, and depth.
- Cubic Yard Calculator — Convert rectangular dimensions in feet to cubic yards.
- Slope Calculator — Calculate the slope between two points on a line.
Related explanations
Learn the method behind the number or compare the terminology before using the calculator.
- How to Calculate Salary from an Hourly Rate — Convert hourly pay into weekly, monthly, and annual estimates and understand the assumptions behind the result.
- How to Calculate Percentage Change — Learn the percentage change formula, how to calculate increases and decreases, and why the original value matters.
- Slope — Learn what slope means and how to calculate the slope between two points.
This page provides a calculation tool plus explanatory information so you can understand what the result means and when the underlying method may not fit your situation.