Roof Pitch Calculator

Find roof pitch, angle and slope factor from rise and run.

Rise

Run

Standard run is 12

Results update as you type.

Pitch (rise per 12 run)

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Angle—

Slope factor—

How it works

Roof pitch describes how steep a roof is, and this calculator converts a simple rise and run measurement into the three forms builders and roofers use: the pitch expressed as rise-in-12, the angle in degrees, and the slope factor. Pitch is traditionally written as a ratio like 6-in-12, meaning the roof rises six inches for every twelve inches of horizontal distance, and the calculator produces this figure from whatever rise and run you measure. The angle in degrees is useful for cutting rafters and setting equipment, while the slope factor is the multiplier that turns a roof's flat footprint area into its true sloped surface area, essential for estimating shingles, underlayment, and other materials accurately, since a steeper roof has more surface than its plan area suggests. Pitch also affects drainage, snow shedding, the choice of roofing material, and whether a roof is walkable. Roofers, framers, and homeowners planning a re-roof use these numbers to order materials and communicate the roof's steepness clearly. You can measure rise and run with a level and tape, or read them from plans. Enter the rise and the run, using 12 for the run if you want a direct rise-in-12 reading.

Formula

pitch = rise/run × 12; angle = arctan(rise/run); slope factor = √(rise² + run²)/run

Roof pitch is usually expressed as the rise in inches for every 12 inches of horizontal run, so dividing rise by run and multiplying by 12 converts any rise and run into that standard form. The roof angle in degrees is the arctangent of rise over run. The slope factor is the length along the sloped roof surface per unit of horizontal run, found from the Pythagorean theorem, and is used to convert flat plan areas into actual roof areas.

Source:Roof geometry (rise, run and slope)

We review all our tools from time to time to ensure accuracy.

Worked example

Rise:6Run:12

A 6-in-12 pitch is an angle of about 26.57° with a slope factor of about 1.118.

How to use this calculator

1
Enter your values
Enter rise and run.
2
Adjust the options
Fine-tune any options to match your situation.
3
Read your result
Pitch (rise per 12 run) updates instantly as you type — no button to press.

Frequently asked questions

How is roof pitch expressed?

Roof pitch is most often written as a ratio of rise to run, such as 6-in-12 or 6:12, meaning the roof climbs six inches vertically for every twelve inches of horizontal distance. This convention lets builders describe steepness in a standard, comparable way. The calculator converts any rise and run you measure into this rise-in-12 form, plus the equivalent angle in degrees.

What is the slope factor used for?

The slope factor converts the flat, plan-view area of a roof into its actual sloped surface area. Because a pitched roof surface is longer than its horizontal footprint, you must multiply the footprint area by the slope factor to estimate materials like shingles and underlayment correctly. A steeper pitch has a larger slope factor and therefore more surface area to cover than the plan suggests.

How do I measure rise and run?

Hold a level horizontally against the roof, mark a run of 12 inches along it, then measure straight down from the level's far end to the roof surface to get the rise over that run. Alternatively, read rise and run from architectural plans. Enter both into the calculator; using a run of 12 gives the pitch directly in the standard rise-in-12 form.

What is a typical roof pitch?

Most residential roofs fall between about 4-in-12 and 9-in-12. Low-slope roofs below roughly 3-in-12 need special membranes because shingles may not shed water well, while steep roofs above 9-in-12 shed snow and water readily but are harder and less safe to walk. The right pitch depends on climate, roofing material, and architectural style.

How does pitch affect material quantities?

A steeper pitch increases the actual roof surface area relative to the building's footprint, so you need more roofing material than the plan area alone would suggest. Multiply the flat footprint by the slope factor to get the true area, then add waste. Ignoring pitch would under-order shingles and underlayment, which is why the slope factor matters for accurate estimating.