Calculate cross slope from edge elevations, known drop and width, or find the required edge drop for a target slope in ft, m, or in.
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Cross Slope Formula
Cross Slope (%) = (Drop / Width) * 100
- Drop — vertical elevation difference between the two edges
- Width — horizontal distance between those edges
- Cross Slope — side-to-side slope, expressed as a percent
For the "Set edge drop" mode, the formula rearranges to:
Drop = Width * (Cross Slope / 100)
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
Use these as reference points. Always check the governing spec for your project.
| Surface | Typical Cross Slope |
|---|---|
| ADA accessible route / sidewalk | Max 2.0% (1:48) |
| 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%. That is under the 2% ADA limit.
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 2.083%, which is why ADA-compliant surfaces are often built to 1:48 instead of an exact 2.0% to 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? Technically yes, but flat surfaces pond water. Most specs require at least 1% to drain.
