Site slope Calculator: measuring notes and method
Use rise and horizontal distance
Measure the vertical difference between two levels and their horizontal separation. A rise of 0.5 m over 10 m is a 5% gradient.
Read percent and degrees separately
Five percent means five units vertically for every hundred horizontally; it does not mean five degrees. A single gradient does not describe a surface with changing levels or determine drainage performance.
CHECK A PRACTICAL EXAMPLE
Same level change, different horizontal run
The measured rise is 300 mm. Change only the horizontal distance.
6 m horizontal run
- Gradient
- 5 %
- Slope angle
- 2.862 °
12 m horizontal run
- Gradient
- 2.5 %
- Slope angle
- 1.432 °
Doubling the horizontal run halves the percentage gradient. Use horizontal distance, not the distance along the sloping surface.
Fixed comparison in metric units. Values are illustrative unless linked to a recorded project; changing the calculator above does not change this example.
Formula
Gradient (%) = rise ÷ horizontal run × 100. Angle = arctan(rise ÷ run).
Worked examples in metric and imperial units
Illustrative values match Reset example and stay fixed when you edit the calculator. Both columns describe the same calculation; converted inputs are rounded.
Metric worked example
- Vertical rise or fall
- 0.3 m
- Horizontal run
- 6 m
Gradient: 5 %
Imperial worked example
- Vertical rise or fall
- 0.9843 ft
- Horizontal run
- 19.685 ft
Gradient: 5 %
Follow the calculation
Lengths in this working are in metres.
- Gradient = 0.3 ÷ 6 × 100 = 5%.
- Angle = arctan(0.3 ÷ 6) = 2.862405°.
Reviewed 19 October 2026. How calculations are checked · Report a correction