CalcCommonsHow to use
Choose the value you know: rise per 12, angle, or measured rise. Enter the horizontal run in the selected unit. Read the equivalent slope and geometric length; measure from a safe location rather than climbing onto a roof to use the tool.
For related tasks, try the Right Triangle Calculator.
Formula & how it works
Slope = rise ÷ run. Rise per 12 = 12 × slope. Angle = arctan(slope). Slope percent = 100 × slope. Slope length = run × √(1 + slope²).
Worked examples
Example 1
A 6:12 slope rises 6 ft over a 12 ft horizontal run. Its angle is about 26.565°, its slope is 50%, and the slope length is about 13.416 ft before overhangs.
Example 2
For a rise of 1 m and a run of 4 m, slope is 0.25: a 3:12 pitch, 25% slope and an angle of about 14.036°.
Assumptions & practical notes
Here, pitch uses the common roofing rise-per-12 convention. Some references use pitch to mean rise divided by full span; that is not the convention shown here.
Use the horizontal run of one roof face. A symmetrical gable’s run is half its span, but do not assume symmetry for every roof.
Slope length is geometric. No overhang, ridge allowance, birdsmouth cut, snow/wind load or structural sizing is included.
See our calculation methodology for unit definitions and testing practices.
Results are estimates for planning purposes. Verify measurements, product specifications, and applicable building codes before purchasing materials or starting work.
References & measurement guidance
Use the instructions for your selected product and the requirements that apply to your project. Example inputs are not universal specifications.
Frequently asked questions
Is 6:12 the same as 6 degrees?
No. A 6:12 slope is 6 divided by 12, or 50%. Its angle is about 26.565 degrees.
What is the difference between run and span?
Run is the horizontal distance for one slope. Span is the overall distance across the roof or building; for a symmetrical gable, span is twice the run.
Can I calculate shingles here?
This tool converts slope measurements. Roof area, waste, shingles and other materials belong to a separate roofing estimate.
Can the roof be flat?
A zero rise produces zero slope and a slope length equal to the run. This mathematical result is not a drainage or roofing-system recommendation.
Related calculators
Right Triangle Calculator
Solve a right triangle from two sides or one side and an acute angle.
Stair Calculator
Plan a straight stair flight: calculate risers, tread count, equal riser height, and horizontal run from finished-floor measurements.
Area Calculator
Calculate the area of six geometric shapes with conversions to common square units.