How to calculate slope grade
Grade is the steepness of a slope as a percentage: grade % = rise ÷ run × 100, where rise is the vertical change and run the horizontal distance. A 3 ft rise over 100 ft of run is 3 ÷ 100 = 3%. The matching angle is arctan(rise ÷ run), about 1.72°. For the algebraic version of the same rise over run between two points, use the slope calculator.
How to use this calculator
Enter the rise and the run in the same units. The result shows the grade percentage and the angle in degrees. Keep rise and run consistent — both in feet, or both in metres.
Where grade is used
Grade describes roads, driveways, drainage and land. Driveways are often kept under 12–15%, and good drainage needs a slight slope away from buildings. For an accessibility ramp expressed as a ratio, use the ramp calculator; for roof steepness, the roof pitch calculator.
For drainage, the usual target is a fall of about 6 inches over the first 10 feet away from a foundation, which is a 5% grade. Paving generally needs at least 1 to 2% so water runs off instead of ponding.
Frequently asked questions
- How do I calculate grade?
- Divide the rise by the run and multiply by 100. A 3 ft rise over 100 ft is a 3% grade.
- What is the difference between grade and angle?
- Grade is a percentage (rise ÷ run × 100); the angle is its arctangent in degrees. A 3% grade is about 1.72°.
- What grade is too steep for a driveway?
- Most guidance keeps driveways under about 12–15%. Steeper slopes can scrape vehicles and become hazardous in ice.
- Do rise and run need the same units?
- Yes. Use feet for both or metres for both, since grade is a ratio of the two.
- How do I convert a grade percentage into a ratio?
- Divide 100 by the grade. A 5% grade is 100 divided by 5, or 1:20, and a 3% grade is 1:33. Ratios are common in accessibility and drainage specs, percentages in road and site work.