Roof Pitch Calculator
Convert a roof's rise and run into its pitch as X/12, the angle in degrees, and the slope factor used to size roofing materials.
📐 What is a Roof Pitch Calculator?
Roof pitch describes how steep a roof is, expressed as the number of inches it rises for every 12 inches of horizontal run, written as X/12. A roof pitch calculator converts a measured rise and run into that X/12 pitch, the equivalent angle in degrees, and a slope factor, the ratio between the roof's true sloped surface area and the flat footprint area of the building underneath it.
Builders framing a new roof, homeowners researching a re-roofing quote, and DIYers checking whether an existing roof matches a shingle manufacturer's slope requirements all use this conversion regularly. Roof pitch determines what roofing materials are even allowed (very low pitches need a waterproof membrane instead of standard shingles), how much material a job needs, and how steep and dangerous the roof is to work on.
A common point of confusion is mixing up pitch, angle, and slope percentage, three different but related ways of describing the same steepness. A 6/12 pitch, a 26.57 degree angle, and a 50 percent slope are all the same roof described three ways, pitch is the carpentry convention, degrees are the trigonometric measure, and percentage is common in civil engineering and drainage design.
Enter the rise and run of the roof, in any consistent units, and this calculator returns the pitch as X/12, the pitch angle in degrees, and the slope factor you can multiply by a building's footprint to estimate the true roof surface area, along with a scaled diagram of the rise-run-roof triangle.
📐 Formula
📖 How to Use This Calculator
Steps
💡 Example Calculations
Example 1 — A Standard Residential Roof
6 inches of rise over a 12 inch run (a "6/12 pitch")
Example 2 — A Steep Roof
9 inches of rise over a 12 inch run (a "9/12 pitch")
Example 3 — A Low-Slope Roof
4 inches of rise over a 12 inch run (a "4/12 pitch")
❓ Frequently Asked Questions
🔗 Related Calculators
How do I calculate roof pitch from rise and run?
Divide the rise by the run and multiply by 12 to express the pitch as X per 12 inches. A roof that rises 6 inches over a 12 inch run has a pitch of (6/12) x 12 = 6, written as a 6/12 pitch.
How do I convert roof pitch to degrees?
Take the arctangent of rise divided by run. A 6/12 pitch has an angle of arctan(6/12) = 26.57 degrees, a 9/12 pitch is arctan(9/12) = 36.87 degrees, and a 12/12 pitch, a 45-degree roof, is arctan(12/12) = 45 degrees exactly.
What is the roof slope factor and what is it used for?
The slope factor is the ratio of the true sloped roof area to the flat footprint area below it, calculated as the square root of rise squared plus run squared, divided by the run. Multiply your building's footprint area by this factor to get the actual roof surface area for ordering shingles or underlayment.
What does a 6/12 roof pitch mean?
A 6/12 pitch means the roof rises 6 inches vertically for every 12 inches (1 foot) of horizontal run. It is one of the most common residential roof pitches, giving a moderate 26.57 degree slope that sheds water well without being unusually steep to frame or walk on.
How much more roofing material does a steep pitch need?
Multiply the flat footprint area by the slope factor to find the true roof area. A 6/12 pitch has a slope factor of about 1.118, so it needs about 11.8% more material than the footprint suggests; a 12/12 pitch has a slope factor of about 1.414, needing about 41.4% more.
What is considered a steep roof pitch versus a low pitch?
Pitches below 4/12 are generally considered low-slope and often require special roofing membranes rather than standard shingles. Pitches from 4/12 to 9/12 are typical for most homes, and anything above 9/12, especially 12/12 or steeper, is considered steep and needs extra safety precautions and often specialized labor to install.
How do I measure the rise and run of an existing roof?
Hold a level horizontally against the roof surface (or use a speed square) so it reads exactly 12 inches (or any convenient equal distance) along the roof, then measure the vertical distance from the level down to the roof surface at that point. That vertical measurement is the rise over the chosen run.
What is the difference between roof pitch and roof slope percentage?
Pitch expresses rise over a fixed 12 inch run, like 6/12, the convention used in residential roofing. Slope percentage expresses rise over run as a percentage of any distance, like 50% for the same 6/12 roof, and is more common in civil engineering, drainage, and ramp design.
Why do roofers and engineers use different ways to describe the same slope?
Roof pitch (X/12) evolved as a practical carpentry convention because framing squares are marked in 12ths, making it easy to set a rafter angle on site. Angle in degrees and slope percentage are more universal and easier to use in trigonometric calculations, which is why this calculator reports all three.
Does a steeper roof pitch cost more to build?
Generally yes. A steeper pitch needs more roofing material due to the larger slope factor, more framing lumber for longer rafters, and often higher labor costs because working safely on a steep slope is slower and requires more fall protection than a gentle one.
How is roof pitch related to attic headroom?
A steeper pitch creates more vertical space under the roofline for a given building width, which is why homes wanting a usable attic or vaulted ceiling often choose a steeper pitch like 8/12 or higher, while a flatter pitch like 3/12 or 4/12 leaves very little headroom near the eaves.