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Roof Slope Calculator

Calculate the roof pitch angle, slope percentage, rafter length, and pitch ratio in 12 from the rise and the horizontal run.

About Roof Slope Calculator

Roof slope describes how steeply a roof rises over a horizontal distance. This calculator uses angle = arctan(rise ÷ run) in degrees, slope = rise ÷ run × 100 percent, and rafter length = √(rise² + run²) by the Pythagorean theorem. The pitch ratio is rise ÷ run × 12, written as x : 12, the convention used in North America. Rafter length excludes overhangs, and the run must be greater than zero.

How to use Roof Slope Calculator

  1. Fill in "Rise" and "Horizontal run".
  2. The result appears below and updates as you type.
  3. Copy the result with the copy button, or download it as a file where that is offered.

Questions about Roof Slope Calculator

What does a 4 : 12 roof pitch mean?

The roof rises 4 units for every 12 units of horizontal run, for example 4 inches per foot. That is a slope of 33.3% and an angle of about 18.4 degrees.

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