Grading Slope Calculator

Calculate site grading slope, run-to-rise ratios, and angle.

Site Grading
1

Design Parameters

Vertical Rise/Fall must be entered.

Quick Presets

Standard ADA Slope Limit (1:12)
8.33% slope threshold for ramp elements.

Calculated Outputs

Slope Percentage %
0.00
Slope Angle Degrees
0.00
Slope Ratio (1:x)
1:0

Site Grading & Slope Standards

Civil and landscape engineering rely on site grading to ensure gravity stormwater drainage away from foundations and safe pathways.

Our professional grading slope calculator translates elevation rises and horizontal runs into slope percentages, angles, and ratios to assist in site drainage design and accessibility compliance.

Site Grading Profile Profile diagram showing grading slope and water runoff vectors.

Slope Calculations

Site grading defines the rate of elevation incline or fall. Slope percentage is calculated by dividing the vertical rise/fall height by the horizontal span run, while slope angle in degrees uses the arctangent function.

Slope Percentage (%) = (Rise ÷ Run) × 100
Slope Angle (Degrees) = arctan(Rise ÷ Run) × (180 ÷ π)
Slope Ratio = 1 : (Run ÷ Rise)
Example Driveway Grading:

1. Vertical Incline Rise: 1.5 meters.

2. Horizontal Span Run: 30.0 meters.

3. Slope Percentage: (1.5 ÷ 30.0) × 100 = 5.0%.

4. Slope Angle (Degrees): arctan(1.5 ÷ 30.0) = arctan(0.05) = 2.86°.

5. Slope Ratio: 1 : (30.0 ÷ 1.5) = 1:20 (1 unit vertical change per 20 units horizontal span).

Result: A driveway with 1.5m rise over 30m run has a 5% slope (1:20 ratio) at an angle of 2.86°.

Minimum Grading for Site Drainage

Adequate soil slope is critical to steer stormwater away from building foundations to prevent basement leaks and structural settlement:

  • Adjacent to Foundations: Civil guidelines recommend a minimum 5% to 10% slope away from foundation walls for the first 10 feet (3 meters) of distance.
  • Lawn Areas: A minimum 1% to 2% slope is required to prevent pooling water in grass fields.
  • Paved Walkways: Typically designed with a 1% cross slope to shed water without creating slipping hazards.

Frequently asked questions

What is a safe grading slope away from a building?

Civil guidelines recommend a minimum 5% slope (6 inches of fall over 10 feet) away from foundations for the first 10 feet.

What is the maximum slope for pedestrian walkways?

For pedestrian walkways to be considered accessible (ADA compliant) without handrails, the slope must not exceed 5% (1:20 ratio). Slopes steeper than this are classified as ramps and must follow ramp guidelines.

How do you convert grade percentage to degrees?

To convert slope percentage to degrees, divide the percentage by 100 to get the decimal slope, then take the arctangent of that decimal. Angle = arctan(Grade % ÷ 100).