Slope Calculator
Convert rise and run into grade percent, angle in degrees, and slope ratio. For driveways, drainage, grading, and site work.
How this calculator works
Slope is the ratio of vertical rise to horizontal run, and the calculator reports it three ways at once — as a percent grade, an angle, and a 1-in-X ratio — from a single rise-and-run measurement.
Formula: Grade % = (rise ÷ run) × 100. Angle = arctan(rise ÷ run). Ratio = run ÷ rise, stated 1 : ratio.
Worked example
A 2-foot rise over a 100-foot run:
- Grade: (2 ÷ 100) × 100 = 2%
- Angle: arctan(2 ÷ 100) ≈ 1.15°
- Ratio: 100 ÷ 2 = 1 : 50
Slope reference
| Grade | Angle | Ratio | Use |
|---|---|---|---|
| 1% | 0.57° | 1:100 | Minimum lawn drainage |
| 2% | 1.15° | 1:50 | Paved-surface drainage |
| 8.3% | 4.8° | 1:12 | ADA ramp maximum |
| 12% | 6.8° | 1:8.3 | Steep driveway limit |
How to measure
Measure the horizontal run and the vertical rise between the high and low points with a level line. For a target grade, multiply the run by the grade percent to check the total fall. For accessible ramps specifically, use the Ramp Calculator, which applies ADA landing rules.
Frequently asked questions
What is the difference between grade, angle, and ratio?
They are three ways to state the same slope. Grade is rise over run as a percent (2 percent). Angle is the same slope in degrees (about 1.15 degrees for a 2 percent grade). Ratio expresses it as 1 in X (1:50). This calculator shows all three from one measurement.
What slope do I need for drainage?
A minimum of about 2 percent (a quarter inch per foot) moves water off hard surfaces and away from foundations. Lawns can grade a bit gentler; paved areas often use 1 to 2 percent. Too flat and water ponds; too steep and it erodes.
What grade is too steep for a driveway?
Most codes cap driveway grade around 12 to 15 percent, and steeper than that risks scraping and traction problems, especially in ice. Break long steep runs with a flatter landing near the garage and the street.
How do I measure rise and run on site?
Set a level line from the high point to the low point, measure the horizontal distance (run) and the vertical drop (rise) between the two ends. A string level, laser level, or transit makes this accurate over long distances.
How does percent grade relate to inches per foot?
One percent grade is about ⅛ inch of drop per foot of run; 2 percent is about ¼ inch per foot. Multiply the per-foot drop by your run to check the total fall matches your target.
Estimates only. Verify quantities with your supplier before purchasing.