Roof Pitch Calculator
Roof pitch expresses vertical rise relative to horizontal run. Builders commonly describe pitch as a rise amount for every 12 units of horizontal run.
How to use this calculator
- Enter rise and horizontal run in the same units.
- Check that all inputs use the same units, period and population scope.
- Change one assumption at a time when comparing scenarios.
Formula used by roof pitch calculator calculator
Pitch per 12 = rise ÷ run × 12; angle = arctan(rise ÷ run).
- Pitch per 12 = rise ÷ run × 12; angle = arctan(rise ÷ run).
- This geometry estimate does not verify structure, drainage, roofing suitability or building-code requirements.
- The tool validates inputs and rounds displayed figures for readability; it does not validate assumptions against external records.
Worked examples
Worked example
A rise of 4 units over a 12-unit horizontal run is a 4:12 pitch.
Rise/run = 4/12; pitch is 4:12 and angle is about 18.43°.
The calculator returns pitch ratio, percent slope and angle.
Understanding the result
Roof pitch expresses vertical rise relative to horizontal run. Builders commonly describe pitch as a rise amount for every 12 units of horizontal run.
This geometry estimate does not verify structure, drainage, roofing suitability or building-code requirements.
Important notes
This geometry estimate does not verify structure, drainage, roofing suitability or building-code requirements.
Treat the result as an estimate from the entered assumptions. For safety, legal, engineering, health or commercial decisions, verify relevant specifications and professional guidance.
Frequently asked questions
Is run measured along the roof?
No. Run is the horizontal distance; roof surface length is the hypotenuse.
Does pitch determine roof safety?
No. Structural design, loads, material and local rules require separate assessment.
How should I interpret this result?
This geometry estimate does not verify structure, drainage, roofing suitability or building-code requirements.
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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.