Calculate road or pavement crossfall, edge drop, or width with metric and imperial units, plus 1:n ratio, angle, per-unit fall, and crowned-section levels.
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Crossfall Formula
The crossfall calculator uses the relationship between horizontal distance, vertical distance, and slope percentage. Crossfall is the vertical change across a given horizontal width, expressed as a percentage.
- CF = crossfall percentage
- V = vertical distance, rise, fall, or height difference
- H = horizontal distance or width across the slope
If you enter horizontal distance and vertical distance, the calculator finds the crossfall percentage. If you enter horizontal distance and crossfall percentage, it finds the vertical distance. If you enter vertical distance and crossfall percentage, it finds the horizontal distance.
The distance units can be different. The calculator converts the entered distances to meters for the calculation, then converts the missing distance back to the unit you selected.
Common Crossfall Percentages
Crossfall is often used for roads, paths, paved areas, and drainage surfaces. The right value depends on the surface, design standard, and drainage requirement.
| Crossfall | Equivalent Ratio | Vertical Fall Over 1 m | Typical Interpretation |
|---|---|---|---|
| 1% | 1 in 100 | 10 mm | Very gentle fall |
| 2% | 1 in 50 | 20 mm | Common drainage crossfall |
| 2.5% | 1 in 40 | 25 mm | Moderate fall |
| 5% | 1 in 20 | 50 mm | Steeper surface fall |
Distance Unit Conversions Used
| Unit | Meters | Use in Calculation |
|---|---|---|
| 1 centimeter | 0.01 m | Small vertical falls |
| 1 foot | 0.3048 m | Imperial site measurements |
| 1 yard | 0.9144 m | Longer imperial distances |
| 1 kilometer | 1000 m | Large horizontal distances |
| 1 mile | 1609.34 m | Large imperial distances |
Example Crossfall Calculations
Example 1: Find crossfall percentage
You have a horizontal distance of 4 m and a vertical fall of 80 mm.
Convert 80 mm to meters:
Apply the crossfall formula:
The crossfall is 2%.
Example 2: Find vertical distance
You have a horizontal distance of 12 ft and a crossfall of 2.5%.
The vertical distance is 0.3 ft, which is 3.6 inches.
FAQ
What does crossfall mean?
Crossfall is the sideways slope across a surface. It describes how much the surface rises or falls across its width. For example, a pavement that drops 20 mm across 1 m has a 2% crossfall.
Is crossfall the same as gradient?
Crossfall is a type of gradient, but it usually refers to slope across the width of a road, path, or paved area. Gradient can refer to slope in any direction, including along the length of a road or surface.
How do you convert crossfall percent to a ratio?
Divide 100 by the crossfall percentage. For example, a 2% crossfall is 100 ÷ 2 = 50, so the ratio is 1 in 50. A 2.5% crossfall is 100 ÷ 2.5 = 40, so the ratio is 1 in 40.
