Road gradients, wheelchair ramps, roofs, drainage pipes and hiking trails all use slope percentages. A 100% slope is a 45° angle – rise equals run – not a vertical wall. Building codes usually limit ramps to 1 : 12 (8.33%).
How to use the Slope Percentage Calculator
- Rise (vertical change)
- Run (horizontal distance)
- Every result field is editable: type into Slope percentage or any other result and Rise (vertical change) plus every other field update to match.
Results update as you type, and everything is calculated in your browser.
How it works
Divide the vertical rise by the horizontal run and multiply by 100. The angle is the arctangent of rise/run. Type a percentage or an angle into the results to find the matching rise for the run you entered.
Inputs explained
| Field | What to enter |
|---|---|
| Rise (vertical change) | Units: cm, m, mm, in, ft, yd … |
| Run (horizontal distance) | Units: cm, m, mm, in, ft, yd … |
What each result means
- Slope percentage = [Rise (vertical change)]÷[Run (horizontal distance)]×100
- Angle = deg(atan([Rise (vertical change)]÷[Run (horizontal distance)]))
- Ratio 1 : n = [Run (horizontal distance)]÷[Rise (vertical change)]
- Slope length = sqrt([Rise (vertical change)]^2 + [Run (horizontal distance)]^2)
Example values
How the main result changes when Rise changes and everything else stays at the example values above:
| Rise (vertical change) (cm) | Slope percentage (%) |
|---|---|
| 12.5 | 4.1667 |
| 18.75 | 6.25 |
| 25 | 8.3333 |
| 31.25 | 10.4167 |
| 37.5 | 12.5 |
| 50 | 16.6667 |
Formula
Slope % = rise ÷ run × 100
Angle = arctan(rise ÷ run)
Ratio = 1 : (run ÷ rise)
Worked example
Inputs — Rise (vertical change): 25 cm; Run (horizontal distance): 300 cm.
Results — Slope percentage = 8.3333 %; Angle = 4.7636 °; Ratio 1 : n = 1 : 12.000; Slope length = 301.04 cm.
Key terms
- Grade
- Another name for slope percentage.
- Run
- The horizontal distance covered.
Frequently asked questions
Is a 100% slope vertical?
No – 100% means the rise equals the run, an angle of 45°. A vertical wall has an infinite slope percentage.
How do I convert a slope percentage to degrees?
Angle = arctan(percentage ÷ 100). 10% ≈ 5.71°.
What is a 1 : 12 slope?
A rise of 1 for every 12 of run, about 8.33% or 4.76° – the usual maximum for wheelchair ramps.
Can a slope be negative?
Yes, a negative rise means downhill.