Slope Gradient Calculator
I know the
Measured level, not along the slope
Slope
8.33%
- Angle
- 4.76°
- Ratio
- 1 : 12
- Horizontal : vertical
- 12H : 1V
- Drop per 100 ft or m
- 8.33
For every 1 unit up, the slope runs 12 units across; 1 inch per foot is 8.33%.
For comparison
- 8.33% — Steepest ADA wheelchair ramp (1:12, 8.33%)
- 6% — Steep grade on an interstate highway (about 6%)
Benchmarks are typical U.S. values; local codes govern.
Convert a slope between rise over run, percent grade, angle in degrees and ratio, and compare it with common limits such as wheelchair ramps, driveways, highways and drainage.
Formula
Worked Example
1 ÷ 12 = 0.0833, an 8.33% grade, and arctan(0.0833) = 4.76°. A 1:12 slope is the steepest the ADA allows for a wheelchair ramp, 1 inch of rise per foot of run.
Frequently Asked Questions
How do I convert percent grade to degrees?
Take the arctangent of the grade as a decimal: 10% is arctan(0.10) = 5.71°, 50% is 26.6° and 100% is 45°, a rise equal to the run. Percent and degrees are not proportional, so 100% is not 90°.
What is the maximum slope for a wheelchair ramp?
1:12 (8.33%) under the 2010 ADA Standards, with a rise of no more than 30 in per run and level landings between runs. Gentler slopes such as 1:16 or 1:20 are easier for most users.
What slope does a drain or patio need?
Ground next to a house should fall at least 6 in in the first 10 ft (5%) under the International Residential Code. Patios commonly slope ⅛–¼ in per foot (1–2%). Under the same code, drain pipes of 2½ in or less need at least ¼ in per foot and 3–6 in pipes at least ⅛ in.