Slope & Grade Calculator
Input Values
Grading targets: standard lawn drainage is 1.5% to 2%, patios should slope 1% to 2% away from structures, and maximum recommended driveways are 12% to 15%.
Slope Calculator: Percent Grade, Angle, and Ratio
Getting drainage right starts with knowing your actual slope — too flat and water pools, too steep and you get erosion or an unsafe surface. Our free slope calculator takes a rise and run measurement and instantly converts it into percent grade, angle in degrees, and a rise-to-run ratio, so you can check your numbers against drainage, driveway, and ADA ramp standards.
How the Slope Calculator Works
Slope is a pure ratio of vertical rise to horizontal run, so no waste buffer or material estimate applies here — this calculator is purely a conversion tool. Enter your rise and run using the same unit for both (inches, feet, centimeters, or meters — it doesn't matter which, as long as they match), and it returns your grade as a percentage, the angle in degrees, and the simplified rise-to-run ratio.
Slope Guidelines by Project Type
| Project | Recommended Grade | Notes |
|---|---|---|
| Lawn drainage | 1–2% | Below 1% risks standing water |
| Driveway | 2–15% | Above ~15% can be difficult in ice/rain |
| ADA-compliant ramp | Max 8.33% | 1:12 rise-to-run ratio, per code |
| Retaining wall likely needed | Over 25% | Grade too steep for turf alone |
Percent Grade vs. Degrees vs. Ratio
These three numbers describe the same slope in different ways. Percent grade is rise divided by run, expressed as a percentage — the most common format for drainage and construction specs. Degrees measure the actual angle from horizontal, more familiar for visualizing steepness. Ratio (like 1:12) expresses how much horizontal run it takes to gain one unit of rise — the format most often used in ADA and building code documents.
Frequently Asked Questions
What is a good slope for lawn drainage?
A grade of 1% to 2% is generally ideal — enough to move water away from structures without causing erosion. Below 1%, water tends to pool; above 5%, mowing becomes noticeably harder.
What is the maximum slope for an ADA ramp?
ADA guidelines require a maximum slope of 8.33%, equivalent to a 1:12 rise-to-run ratio — meaning 12 inches of horizontal run for every 1 inch of rise.
How steep can a driveway be?
Most residential driveways stay under 15% grade for safe vehicle traction, especially in wet or icy conditions. Steeper driveways are possible but become increasingly difficult and may need special surface treatments.
Do I need to use feet for rise and run?
No — any unit works as long as both rise and run use the same one. Inches, feet, centimeters, or meters will all produce the same percent grade and angle results.
At what slope do I need a retaining wall instead of just grading?
There's no single hard cutoff, but grades over roughly 25–33% become difficult to maintain with turf or plantings alone, and a retaining wall or terracing is commonly used to manage the grade change safely.
Related Calculators
Planning a full landscaping project? These calculators pair well with slope and grade checks:
French Drain Calculator — plan drainage for areas where water pools due to grade.
Retaining Wall Calculator — design a wall to manage a steep grade change.
Fence Calculator — account for slope when planning post depth and fence layout.