30 percent: a steep bank
30% is 16.70°, about 1 in 3.33. It rises 3.6 inches per foot, 30 feet over 100 feet, three times the 10% at the top of the usual driveway range.
The slope length starts to matter here: 100 feet on the plan is 104.40 feet on the ground, so mulch, seed or erosion fabric for a bank this steep should be measured along the slope.
A bank that runs back 20 feet at 30% stands 6 feet high.
30% slope: rise over a distance
A 30% slope rises 30 feet in every 100 feet of level distance.
| Run (level distance) | Rise in inches | Rise in feet | Length along the slope |
|---|---|---|---|
| 1 ft | 3.6 in | 0.3 ft | 1.04 ft |
| 10 ft | 36 in | 3 ft | 10.44 ft |
| 20 ft | 72 in | 6 ft | 20.88 ft |
| 50 ft | 180 in | 15 ft | 52.20 ft |
| 100 ft | 360 in | 30 ft | 104.40 ft |
Worked example
30 ÷ 100 = 0.3. The angle is the arctangent of that: arctan(0.3) = 16.70°. As a ratio, 100 ÷ 30 = 3.33, so the slope is 1 in 3.33. Per foot, 0.3 × 12 = 3.6 inches.
Nearby grades in degrees
| Grade | Angle | Ratio | Rise per foot |
|---|---|---|---|
| 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 |
| 50% | 26.57° | 1 in 2 | 6 in |
| 100% | 45.00° | 1 in 1 | 12 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
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Frequently asked questions
What is a 30 percent slope in degrees?
16.70 degrees. Divide the percent by 100 and take the arctangent: arctan(0.3) = 16.70°.
How steep is a 30 percent slope?
16.70°, about 1 in 3.33: 3.6 inches of rise per foot, or 30 feet in 100 feet.
How much does a 30% slope rise per foot?
3.6 inches for every foot of run, which is 36 inches over 10 feet and 30 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.