Slope Percentage Calculator
Calculate slope grade, angle, and incline percentage
How to Use This Calculator
Choose Method
Select whether you know the rise/run, angle, or ratio.
Enter Values
Input your measurements in consistent units.
View All Formats
See slope expressed as percentage, angle, and ratio.
Formula
Slope Percentage = (Rise / Run) × 100
Slope Angle = arctan(Rise / Run) × (180 / π)
Example 1: Wheelchair ramp - 2 ft rise, 24 ft run
Percentage = (2 / 24) × 100 = 8.33%
Angle = arctan(2/24) × (180/π) = 4.76°
This is the maximum ADA recommended slope
Example 2: Roof pitch - 4 inch rise per 12 inch run
Percentage = (4 / 12) × 100 = 33.33%
Angle = arctan(4/12) × (180/π) = 18.43°
Common residential roof pitch (4:12)
Example 3: Road grade - 45° angle
Percentage = tan(45°) × 100 = 100%
Rise equals run (1:1 ratio)
About Slope Percentage Calculator
The Slope Percentage Calculator (also called grade calculator or incline calculator) helps you determine the steepness of a surface. This tool is essential for construction, landscaping, road design, accessibility planning, and many other applications.
When to Use This Calculator
- ADA Compliance: Ensure ramps meet accessibility standards (max 8.33% or 1:12)
- Road Construction: Design and grade roadways safely
- Roof Design: Calculate roof pitch for proper drainage
- Landscaping: Plan drainage and terracing
- Trail Building: Design hiking and biking trails
- Parking Lots: Ensure proper drainage slopes (1-5%)
- Driveways: Check if grade is manageable for vehicles
Common Slope Standards
- ADA Ramps: Maximum 8.33% (1:12 ratio)
- Commercial Ramps: 5-8% recommended
- Residential Ramps: 6.25% or less preferred
- Parking Lots: 1-5% for drainage
- Walkways: 2-5% comfortable range
- Driveways: 10-15% maximum
- Roads: Varies by location, typically 6-12%
Understanding Slope Measurements
Percentage: Most common in construction. A 10% slope means 10 units of rise per 100 units of run.
Ratio: Common in roofing (e.g., 4:12 pitch). The first number is rise, second is run.
Angle: Used in engineering. A 45° angle equals 100% slope.
Real-World Applications
Wheelchair Ramp: Building codes require maximum 1:12 ratio (8.33%). For a 24-inch rise, you need at least 24 feet of run length.
Roof Design: A 6:12 roof pitch (50% slope, 26.57°) is common for residential homes, providing good water runoff and attic space.
Mountain Road: A steep mountain road with 15% grade (8.53°) requires careful driving and may restrict large vehicles.
Tips for Measuring Slope
- Always use consistent units (feet, meters, inches)
- Measure rise and run on the same scale
- For long distances, account for elevation changes
- Check local building codes for required slopes
- Consider drainage when planning slopes
- Safety first - steeper slopes need handrails
Frequently Asked Questions
What is the ADA maximum slope?
The ADA (Americans with Disabilities Act) maximum slope for wheelchair ramps is 1:12 ratio, which equals 8.33% or approximately 4.76°.
How do I convert roof pitch to percentage?
Divide the rise by the run and multiply by 100. For example, a 4:12 pitch = (4/12) × 100 = 33.33% slope.
Is a 20% slope steep?
Yes, a 20% slope (11.3°) is quite steep. It is challenging to walk and may be difficult for vehicles. Most driveways should not exceed 15%.
What units should I use?
Any units work as long as rise and run use the same unit (both feet, both meters, both inches, etc.).
Can slope percentage exceed 100%?
Yes! A 100% slope means rise equals run (45° angle). Slopes over 100% are steeper than 45 degrees.