How it works
Grade (%) = rise ÷ run × 100. Angle = atan(rise ÷ run). Ratio = 1 : (run ÷ rise).
- Choose the measurements you know.
- Use the same unit for all lengths.
- Read the grade, angle and run per unit rise.
Worked example: A rise of 1 metre over a horizontal run of 12 metres gives 1 ÷ 12 × 100 = 8.33%. The angle is 4.76° and the ratio is 1 : 12.
Common slope grades
| Given | Grade | Angle | Ratio | Input |
|---|---|---|---|---|
| Ratio 1 : x | 8.33% | 4.76° | 1 : 12 | 1 : 12 |
| Ratio 1 : x | 5% | 2.86° | 1 : 20 | 1 : 20 |
| Rise and run | 10% | 5.71° | 1 : 10 | Rise 1, run 10 |
| Angle in degrees | 100% | 45.00° | 1 : 1 | 45° |
| Percentage grade | 5% | 2.86° | 1 : 20 | 5% |
| Angle in degrees | 57.74% | 30.00° | 1 : 1.7321 | 30° |
Swipe the table sideways to see the rest.
Things to consider
- Measure horizontal run, not sloped distance.
- Use absolute rise for a descending slope.
- Check local codes before designing a ramp.
- Angle or grade alone cannot determine actual lengths.
Frequently asked questions
How do I calculate slope percentage?
Divide vertical rise by horizontal run, then multiply by 100. Keep both measurements in the same unit. A rise of 1 over a run of 12 gives 8.33%.
What is the difference between slope percentage and degrees?
Percentage describes rise per 100 units of horizontal run. Degrees describe the angle to horizontal. Grade = tan(angle) × 100, so 30° is about 57.74%, not 30%.
What is a 100% slope?
It rises one unit for every one unit of horizontal run, giving a 45° angle and a 1 : 1 ratio. It is not vertical. A vertical slope has zero run and no finite percentage grade.
What are common grades for ramps, roads and roofs?
Ramps often use 1 : 12, about 8.33%, but accessibility rules vary by country and use. Check local codes. Roads are usually under about 10%, although steeper sections exist. Roofs are often described by pitch, meaning rise over horizontal run.
How do I measure rise and run?
Measure the vertical height difference and the horizontal distance between the same endpoints. A tape along the slope measures sloped length, not run. If you know rise and sloped length, run = √(length² − rise²).
How do I show a descending or level slope?
Enter the absolute height difference for a descent. This calculator reports the magnitude rather than a signed grade. Zero rise gives 0% and 0°, with no finite 1 : x ratio.
Results are estimates for general information only, not financial, medical or professional advice.