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Roof Pitch Calculator

Use this roof pitch calculator entirely in your browser.

ResultRoof pitch angle: 26.57°

Pitch ratio: 6.00 in 12

Slope length for the entered run: 13.42 units

Slope factor: 1.1180

This geometry does not size rafters, determine drainage, or establish structural or code compliance.

Calculations happen locally in your browser.

How to use this calculator

  1. Enter the labelled values and review the live result.
  2. Review the live result and use Copy result when you need to share it.

How the calculation works

The angle is arctangent of rise divided by run; Pythagoras gives the corresponding slope length.

Formula

Angle = arctan(rise ÷ run); slope length = √(rise² + run²)

Step-by-step calculation

  1. Enter the labelled values and review the live result.
  2. The angle is arctangent of rise divided by run; Pythagoras gives the corresponding slope length.
  3. Check the displayed result, then copy it if needed.

Worked example

A rise of 6 over a run of 12 produces a 26.57° angle and a 6-in-12 pitch.

Methodology and review

Who this is for

People converting roof rise and run into angle and slope length.

Inputs and units

  • Rise
  • Run
  • Optional span units

Method

Pitch angle is arctangent of rise divided by run; slope length follows the Pythagorean theorem.

Worked example

A 6-in-12 pitch has an angle of about 26.6°.

Assumptions

  • Rise and run form a right triangle.
  • Measurements describe one uniform roof plane.

Common mistakes

  • Using total span instead of horizontal run
  • Treating pitch as structural approval

Limitations

  • Loads, spans, drainage, coverings, and code compliance are not assessed.
  • Do not use the result as structural design advice.

How this tool was checked

Tests cover known ratios, zero-rise cases, angle conversion, and slope length.

Reference sources

Related tools

Calculation review: 21 August 2026. Published by Goldwave Dynamics Limited. This is an internal product review, not an independent certification.

Risk guidance

Consistent units are enough

Rise and run may be entered in any matching unit because the angle and ratio depend on their proportion. The slope length is returned in that same unit.

Geometry is not roof design

The result does not size rafters, calculate loads, select coverings, test drainage, or interpret construction requirements. Use project-specific design information.

Frequently asked questions

Does this tool send my inputs anywhere?

No. The interactive calculation runs in your browser and this site does not submit tool inputs to a backend.

How should I use the result?

Use it for early planning only. Verify measurements, definitions, current local requirements, and the complete design with the relevant authority and appropriately qualified professionals.

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