Slope Calculator
Calculate slope percentage, angle and rise-over-run ratio.
Project details
Enter your measurements below.
Read the same slope in the form your project uses
A slope can be described as rise over run, a percentage grade or an angle. Those expressions are related, but they are not interchangeable numbers. This calculator helps translate between them for general layout work such as drainage, landscape grading and non-structural planning. Measure the vertical change and the horizontal run, not the sloped surface length. Roof pitch has its own conventions, so use the roof-specific calculator when the job is actually a roof.
Rise is vertical change; run is horizontal distance.
Slope ratio, percent grade and angle can describe the same measured incline.
The result describes geometry. It does not determine whether a ramp, drain or structure satisfies a code or performance requirement.
How to use the Slope Calculator
- Choose two points on the slope and measure the horizontal run between them.
- Measure the vertical rise or fall between those same points. Keep both measurements in compatible units.
- Calculate rise ÷ run for the slope ratio; multiply by 100 for percent grade or use arctangent for the angle.
- Compare the result with the requirement for your particular project rather than assuming one percentage is suitable for every use.
One measured incline, several ways to describe it
A 0.02 slope ratio, a 2% grade and an angle of about 1.15° represent the same geometry. The useful format depends on the trade or specification you are working from.
Use the number in context
Record both the rise/run measurements and the calculated format. If a project has a minimum or maximum slope requirement, verify that requirement from the appropriate design, manufacturer or local rule.
Worked example: a gentle drainage fall
- Horizontal run
- 20 ft
- Vertical fall
- 0.4 ft (4.8 in)
- Ratio
- 0.4 ÷ 20 = 0.02
- Grade
- 2%
The measured fall is a 2% grade. Its angle is only about 1.15°, which shows why small drainage slopes can look nearly flat while still having a measurable fall.
Practical planning tips
Use a level, laser or reliable elevation reference for small slopes; eyeballing a one- or two-percent grade is difficult.
For long runs with changing grade, take several measurements rather than assuming the endpoints describe every section.
Keep the sign or direction in your notes. A mathematically correct 2% slope in the wrong direction still creates a drainage problem.
Use the Roof Pitch Calculator for roofs because roof work commonly uses rise per 12 units of horizontal run.
Common mistakes to avoid
Using the sloped surface length as the run. Run is the horizontal projection, not the hypotenuse.
Comparing 2 degrees with 2 percent as though they were the same slope.
Converting rise to inches but leaving run in feet before dividing.
Treating a calculated slope as proof that a ramp, drainage system or accessible route meets applicable requirements.
Slope Calculator FAQs
Is a 2% slope the same as 2 degrees?+
No. A 2% grade is about 1.15°. Percent grade and angle are different ways of expressing slope.
What is rise and what is run?+
Rise is the vertical change in elevation. Run is the horizontal distance over which that change occurs.
Can this calculator be used for roof pitch?+
It can describe the geometry, but roof pitch is usually communicated with roof-specific conventions such as rise per 12. The Roof Pitch Calculator is clearer for that use.
Does the calculator tell me the correct drainage slope?+
No. It calculates the slope you measured or entered. The required slope depends on the project, system and applicable specification.