20 percent: a 1 in 5 slope
20% is 11.31°, not 20°: 1 unit up for every 5 along. It rises 2.4 inches per foot and 20 feet over 100 feet, twice the 10% at the top of the usual driveway range.
Along the surface, 100 feet of run measures 101.98 feet. A 24 inch rise needs just 10 feet of run, against 24 feet for a 1:12 ramp.
A bank that runs back 25 feet at this grade is 5 feet high.
20% slope: rise over a distance
A 20% slope rises 20 feet in every 100 feet of level distance.
| Run (level distance) | Rise in inches | Rise in feet | Length along the slope |
|---|---|---|---|
| 1 ft | 2.4 in | 0.2 ft | 1.02 ft |
| 10 ft | 24 in | 2 ft | 10.20 ft |
| 20 ft | 48 in | 4 ft | 20.40 ft |
| 50 ft | 120 in | 10 ft | 50.99 ft |
| 100 ft | 240 in | 20 ft | 101.98 ft |
Worked example
20 ÷ 100 = 0.2. The angle is the arctangent of that: arctan(0.2) = 11.31°. As a ratio, 100 ÷ 20 = 5, so the slope is 1 in 5. Per foot, 0.2 × 12 = 2.4 inches.
Nearby grades in degrees
| Grade | Angle | Ratio | Rise per foot |
|---|---|---|---|
| 10% | 5.71° | 1 in 10 | 1.2 in |
| 12% | 6.84° | 1 in 8.33 | 1.44 in |
| 15% | 8.53° | 1 in 6.67 | 1.8 in |
| 20% | 11.31° | 1 in 5 | 2.4 in |
| 25% | 14.04° | 1 in 4 | 3 in |
| 30% | 16.70° | 1 in 3.33 | 3.6 in |
| 33% | 18.26° | 1 in 3.03 | 3.96 in |
For any other rise, run or grade use the slope and grade calculator. The guide slope and grade for drainage and ramps covers how much fall each job needs.
Want to change anything else? The calculator above is the full Slope and Grade Calculator: edit any number and the results update instantly.
Tools & materials for this project
Affiliate links As an Amazon Associate we earn from qualifying purchases. These links do not change what you pay.
Frequently asked questions
What is a 20 percent slope in degrees?
11.31 degrees. Divide the percent by 100 and take the arctangent: arctan(0.2) = 11.31°.
Is a 20 percent slope 20 degrees?
No. A 20% slope is 11.31°, a little over half that. Percent and degrees are different scales.
How much does a 20% slope rise per foot?
2.4 inches for every foot of run, which is 24 inches over 10 feet and 20 feet over 100 feet.
Related sizes and guides
Estimates only. Results assume standard materials and simple shapes. Supplier products vary, and the final call on quantity, structure and safety is yours. Check your local code and your supplier's guidance before ordering.