8.33 percent: the 1:12 ramp
8.33% is the 1:12 slope, 4.76°: 1 inch of rise for every 12 inches along. It is the steepest slope allowed for an accessible ramp under the ADA and most codes, with landings.
A ramp at this slope needs 24 feet of run to rise 24 inches, and its surface is 24.08 feet long. A single 7 inch step needs 7 feet, and a 30 inch porch 30 feet.
Check your local rules, and use a gentler slope where there is room: the limit is a maximum, not a target.
8.33% slope: rise over a distance
An 8.33% slope rises 8.33 feet in every 100 feet of level distance.
| Run (level distance) | Rise in inches | Rise in feet | Length along the slope |
|---|---|---|---|
| 1 ft | 1 in | 0.08 ft | 1.00 ft |
| 10 ft | 10 in | 0.83 ft | 10.03 ft |
| 20 ft | 20 in | 1.67 ft | 20.07 ft |
| 50 ft | 50 in | 4.17 ft | 50.17 ft |
| 100 ft | 100 in | 8.33 ft | 100.35 ft |
Worked example
8.33 ÷ 100 = 0.0833. The angle is the arctangent of that: arctan(0.0833) = 4.76°. As a ratio, 100 ÷ 8.33 = 12, so the slope is 1 in 12. Per foot, 0.0833 × 12 = 1 inch.
Nearby grades in degrees
| Grade | Angle | Ratio | Rise per foot |
|---|---|---|---|
| 1% | 0.57° | 1 in 100 | 0.12 in |
| 2% | 1.15° | 1 in 50 | 0.24 in |
| 5% | 2.86° | 1 in 20 | 0.6 in |
| 8.33% | 4.76° | 1 in 12 | 1 in |
| 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 |
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 an 8.33 percent slope in degrees?
4.76 degrees. Divide the percent by 100 and take the arctangent: arctan(0.0833) = 4.76°.
Is an 8.33 percent slope the same as 1:12?
Yes. 1 ÷ 12 = 0.0833, which is 8.33%, or 4.76°. Every inch of rise takes 12 inches of run.
How much does an 8.33% slope rise per foot?
1 inch for every foot of run, which is 10 inches over 10 feet and 8.33 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.