Roof Pitch Calculator
Convert roof pitch between degrees, percent and the X:12 ratio instantly.
This free roof pitch calculator converts between the three most common ways of expressing a roof's slope: degrees (the angle from horizontal), percent slope (rise divided by run, ×100), and the traditional X-in-12 ratio used by roofers and carpenters in the US and Canada, where the pitch is expressed as inches of rise for every 12 inches of horizontal run.
Roof pitch affects drainage, snow load, material choice and even attic usable space, so getting the conversion right matters when reading architectural drawings, ordering roofing materials, or comparing a pitch specified in one system against a code requirement written in another.
Frequently Asked Questions
What is roof pitch?
Roof pitch describes how steep a roof is — the ratio of its vertical rise to its horizontal run. It can be expressed as an angle in degrees, a percentage, or a traditional X-in-12 ratio.
What does a "6/12 pitch" mean?
It means the roof rises 6 inches for every 12 inches of horizontal run, which corresponds to an angle of about 26.57° and a slope of 50%.
How do I convert degrees to percent slope?
Percent slope = tan(angle in degrees) × 100. For example, a 30° roof has a percent slope of tan(30°) × 100 ≈ 57.7%.
How do I convert percent slope to degrees?
Angle = arctan(percent slope ÷ 100). For example, a 50% slope gives arctan(0.5) ≈ 26.57°.
How is the X-in-12 ratio calculated from degrees?
Rise per 12 = tan(angle in degrees) × 12. A 45° roof, for instance, has a rise of tan(45°) × 12 = 12, so it is described as a 12/12 pitch.
What is considered a low-slope roof?
Roofs with a pitch below about 3/12 (roughly 14°) are generally considered low-slope and often require different roofing materials, such as membrane systems, instead of standard shingles.
What is a steep-slope roof?
Roofs steeper than about 9/12 (roughly 37°) are typically classified as steep-slope, sometimes requiring special safety equipment for installation and maintenance.
Why do roofers use the X-in-12 system instead of degrees?
The 12-inch run makes it easy to measure directly with a standard carpenter's level and tape measure on site, without needing an angle-measuring tool.
Does roof pitch affect material choice?
Yes. Steeper pitches shed water and snow faster and can use a wider range of materials, while low-slope roofs need waterproof membrane systems since water drains more slowly.
How do I find the rise for a specific horizontal run?
Multiply the run by the tangent of the pitch angle (or by the X-in-12 ratio divided by 12). This calculator shows the rise for any run you enter alongside the pitch conversion.