Roof Pitch Calculator

Convert any measured vertical rise and horizontal run into the four roof-slope formats used for geometry and material planning.

Roof pitch conversionOne measured ratio is shown as pitch, angle, percent slope, and surface multiplier.

6 : 12roof pitch (rise : run)

Pitch angle: 26.57°
Slope percentage: 50%
Slope multiplier: 1.118
Rise ÷ run: 0.5

This converts measured geometry only. It does not select a code-compliant pitch, roof system, drainage design, or fall-protection method.

Show calculation

6 rise ÷ 12 run × 12 = 6 in 12; arctan(rise ÷ run) = 26.57°

Transparent method and editable product assumptions. Verify current labels and project requirements.

How this calculator works

Roof pitch is a rise-to-horizontal-run ratio. The calculator divides the measured vertical rise by horizontal run and normalizes that ratio to 12 units of run, producing the familiar x:12 pitch.

The roof pitch angle is the arctangent of rise divided by run. Percent slope is the same ratio multiplied by 100. The slope multiplier is the hypotenuse-to-run ratio, useful for converting a horizontal projection to sloped surface length or area.

Inputs may use any common length unit because rise and run form a dimensionless ratio. The tool converts geometry only; it does not recommend a pitch for drainage, climate, roofing products, code, or safe access.

Formula

Pitch = rise ÷ run × 12; angle = arctan(rise ÷ run); multiplier = √[1 + (rise ÷ run)²]The live substitution appears with your result.

Control example: 6 in rise over 12 in run

The ratio is 6 ÷ 12 = 0.5, so the normalized pitch is 6:12 and the slope is 50%.

arctan(0.5) = 26.57°, and √(1 + 0.5²) = 1.1180 as the slope multiplier.

Assumptions and limits

Rise and run describe the same straight roof plane.
Run is horizontal, not the already-sloped rafter length.
Measurements use the same unit basis.
The roof plane has a constant slope.

Common measuring mistakes

Using full building span as the run of one symmetrical roof side.
Entering rafter length as horizontal run.
Reading a 6:12 pitch as a 50-degree angle.
Using geometric slope as a fall-protection or product-selection decision.

Sources

Product-specific values remain editable. These sources support the method and stated examples; they are not a universal substitute for your supplier’s current label.

OSHA Construction Glossary Defines roof slope using the vertical-to-horizontal 4-in-12 relationship and distinguishes low- and steep-slope roofs.
U.S. Department of Energy roof-pitch example Uses rise/run notation such as 9:12 and 4:12 in roof geometry examples.

Questions people ask

How do I calculate roof pitch?

Divide vertical rise by horizontal run and multiply by 12 to express the result as x:12.

What angle is a 6:12 roof pitch?

A 6:12 pitch is approximately 26.57 degrees above horizontal.

What is roof slope percentage?

It is rise divided by horizontal run, multiplied by 100. A 6:12 pitch is a 50% slope.

What does the slope multiplier do?

It converts horizontal projected length or area to the corresponding straight sloped length or plane area for one constant pitch.

Does this calculator recommend a roof pitch?

No. Product limitations, drainage, climate, structure, code, and safety require project-specific review.