Calculate sidewalk slope as a percent grade, ratio and angle from rise and run, and check it against 1:20 running, 1:48 cross or 1:12 ramp slopes.
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Sidewalk Slope Formula
The calculator runs three modes. Each uses the same rise-run relationship rearranged for the unknown.
- Rise: vertical change between the two ends of the walk
- Run: horizontal distance, not the sloped surface length
- Grade: slope expressed as a percent
- Angle: arctan(Rise / Run), reported in degrees
Rise and run must use compatible units before dividing. Choose inches, feet, centimeters or meters for each measurement; the calculator converts mixed units internally. Use the horizontal run, not a tape pulled along the slope, or the grade reads low.
Sidewalk Slope References
These are planning references from the ADA Standards, including walking surfaces (§403.3), ramp runs (§405.2) and curb ramp flares (§406.3), where those provisions apply. They are not universal limits for every sidewalk. Confirm applicable site, local and public-right-of-way rules, other design requirements and permitted exceptions separately.
| Surface | Grade reference | Ratio | Drop per 10 ft |
|---|---|---|---|
| Running slope, accessible walk | 5% | 1:20 | 6 in |
| Walking surface cross slope | ≈2.0833% | 1:48 | 2.5 in |
| Ramp segment | ≈8.3333% | 1:12 | 10 in |
| Curb ramp flares | 10% | 1:10 | 12 in |
Quick conversion between percent grade, ratio, and angle:
| Grade | Ratio | Angle |
|---|---|---|
| 1% | 1:100 | 0.57° |
| 2% | 1:50 | 1.15° |
| 5% | 1:20 | 2.86° |
| ≈8.3333% | 1:12 | 4.76° |
| 10% | 1:10 | 5.71° |
Worked Example and FAQ
Example. A walkway drops 10 in across 24 ft of horizontal run. Slope = (10 / 288) × 100 ≈ 3.47%, below the selected 1:20 (5%) walking-running reference. Where ADA §403.3 applies, check cross slope separately against 1:48 (approximately 2.0833%). This slope comparison alone does not establish compliance.
What is the difference between running slope and cross slope? Running slope follows the direction of travel. Cross slope runs perpendicular to it and sheds water. Both have separate limits and must be checked independently.
Do I use the sloped surface length or the horizontal distance? Use the horizontal run. For shallow sidewalk grades the difference is small, but the formula is defined that way and code references follow the same convention.
What if my walk exceeds 5%? Where the ADA accessible-route provisions apply, walking surfaces steeper than 1:20 are treated as ramps and additional ramp requirements must be reviewed. Public-right-of-way routes and other sites can have different scoping and exceptions. Confirm the applicable requirements, including rise limits, landings and handrails; this calculator checks only the selected numeric grade reference.
Why does a flat sidewalk still need some slope? Drainage requires a separate review of grading, surfaces and water outlets. A calculated slope alone does not guarantee that water will drain or that the surface meets accessibility requirements. Use the requirements and drainage design applicable to the project.
