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Slope & Grade Calculator

Calculate slope percentage, grade, and angle for drainage and grading.

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Slope & Grade Calculator

For accurate slope measurements, use a string level stretched between two stakes at least 10 ft apart. Measure the vertical drop at the lower stake - a 2% grade equals approximately 1/4 inch drop per foot. Always verify finished grade slopes away from the foundation by a minimum of 6 inches over the first 10 ft.

What This Calculator Does

The Slope and Grade Calculator computes the percent grade, angle in degrees, and ratio from a given rise (vertical change) and run (horizontal distance). Enter the rise and run in feet to instantly see the slope expressed three ways - percent, degrees, and ratio.

Slope and grade calculations are essential for drainage, grading, driveway design, and accessibility ramps. The ADA requires ramps to have a maximum slope of 8.33% (1:12 ratio). Building codes require 1-2% grading away from foundations for proper drainage. Driveways should have a maximum 10% slope for safe vehicle access. Each application uses a different expression of the same calculation.

The calculator provides all three common formats simultaneously so you can apply the result to any standard - whether you're reading a code requirement in degrees, a grading spec in percent, or an ADA guideline in ratio form.

How to Use

  1. Measure the vertical rise of your slope in feet (the total drop or elevation change).
  2. Measure the horizontal run in feet (the distance over which the rise occurs).
  3. Enter both values into the calculator fields above.
  4. Click "Calculate" to get the grade in percent, angle in degrees, and ratio.
  5. Compare your result against the relevant building code requirement.

Worked Examples

1

Driveway Approach Grade Check

A driveway approach for a 40-ft long run with a 3.5-ft total drop from the garage floor to the street, needing verification against the 10% maximum driveway slope.

  1. →Total rise: 3.5 ft. Total run: 40 ft.
  2. →Grade percentage: (3.5 / 40) x 100 = 8.75%.
  3. →Angle in degrees: arctan(3.5 / 40) = 5.0 degrees.
  4. →Ratio: 3.5:40 = 1:11.4 (gentler than 1:10 maximum).
  5. →This grade is within the recommended maximum of 10% for residential driveways.

Result: 8.75% grade, 5.0 degrees angle - acceptable for residential driveway access. Total estimate within code limits.

If your driveway grade exceeds 10%, consider a switchback design or a longer approach path. Driveways steeper than 10% can cause vehicles to scrape and lose traction in wet or icy conditions.

Reference Table

Grade and slope reference - drainage, ramps, and driveway standards
Grade %Angle (deg)RatioApplication
1%0.6deg1:100Minimum drainage
2%1.1deg1:50Foundation drainage standard
5%2.9deg1:20Patio/terrace slope
8.3%4.8deg1:12ADA ramp max
10%5.7deg1:10Driveway max slope
15%8.5deg1:6.7Walkway max slope

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