Calculate cross slope from edge rise and width or find the required crossfall from a target percent, with angle, 1:N ratio, and metric or imperial units.
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Cross Slope Formula
- Signed edge offset — second-edge elevation minus first-edge elevation; negative means a drop
- Width — horizontal distance between those edges
- Cross Slope — side-to-side slope, expressed as a percent
For the edge-difference-from-target-slope mode, the formula rearranges to:
Drop and width must be in the same units before dividing. The calculator converts feet, meters, and inches internally. Cross slope is the tangent of the surface angle, so for the small slopes used in pavement and walkway design it closely matches the angle in radians.
Typical Cross Slope Values
These are illustrative reference values, not universal design limits. ADA §403.3 specifies 1:48 for applicable walking surfaces. Always check the governing specification and exceptions for your project.
| Surface | Typical Cross Slope |
|---|---|
| ADA accessible route / sidewalk | 1:48 maximum (about 2.0833%) under ADA §403.3; verify applicability |
| Standard concrete sidewalk | 1.0% – 2.0% |
| Asphalt roadway (tangent) | 1.5% – 2.0% |
| Gravel or unpaved road | 3.0% – 4.0% |
| Parking lot | 1.0% – 5.0% |
| Driveway (cross slope) | 1.0% – 2.0% |
| Patio away from house | 1.0% – 2.0% |
Quick conversions between how cross slope is commonly expressed:
| Percent | Ratio | In/ft | Angle |
|---|---|---|---|
| 1.0% | 1:100 | 0.12 | 0.57° |
| 2.0% | 1:50 | 0.24 | 1.15° |
| 2.08% | 1:48 | 0.25 | 1.19° |
| 4.0% | 1:25 | 0.48 | 2.29° |
| 5.0% | 1:20 | 0.60 | 2.86° |
Example and Common Questions
Example: A sidewalk is 5 ft wide. The high edge sits at elevation 100.10 ft and the low edge at 100.02 ft. Drop is 0.08 ft. Cross slope = (0.08 / 5) × 100 = 1.6%. Its 1.6% magnitude is below 1:48 (about 2.0833%); this calculation alone does not establish ADA compliance.
Is cross slope the same as running slope? No. Cross slope is perpendicular to the direction of travel. Running slope (or grade) follows the direction of travel.
What does 1:48 mean? One unit of vertical drop for every 48 units of horizontal distance. It works out to about 2.0833%. An exact 2.0% is 1:50 and is slightly flatter; a design at the 1:48 maximum does not itself leave construction tolerance.
How much drop do I need across a 4 ft walkway at 2%? 4 ft × 0.02 = 0.08 ft, or about 15/16 in.
Can cross slope be zero? Zero is a level cross section. Drainage depends on the full surface geometry and project specification; the tool does not assume a universal minimum cross slope.
