Slope Percent Grade Calculator
Convert between slope angle in degrees, percent grade, and rise/run ratio.
Enter any one value to get the others.
Used for roads, ramps, and drainage.
Slope Percent Grade Calculator
Slope can be expressed in three equivalent ways. Enter any one value to instantly calculate the other two.
The Three Slope Measures
| Measure | Formula | Description |
|---|---|---|
| Angle (degrees) | θ = arctan(rise / run) | Standard geometric angle from horizontal |
| Percent Grade | G% = tan(θ) × 100 | Rise per 100 units of horizontal run |
| Rise/Run Ratio | r = tan(θ) | Decimal ratio (0.10 = 10%) |
Converting Between Forms
If you know the angle in degrees:
- Percent Grade = tan(θ°) × 100
- Rise/Run = tan(θ°)
If you know percent grade G:
- Angle = arctan(G / 100)
- Rise/Run = G / 100
If you know rise/run ratio R:
- Angle = arctan(R)
- Percent Grade = R × 100
Common Grade Values
| Angle | Grade | Application |
|---|---|---|
| 1.1° | 2% | Minimum road drainage slope |
| 4.8° | 8.33% | Maximum ADA wheelchair ramp |
| 5.7° | 10% | Steep residential driveway |
| 10° | 17.6% | Challenging cycling climb |
| 26.6° | 50% | Very steep terrain |
| 45° | 100% | Equal rise and run |
Important Note
Percent grade is NOT the same as angle in degrees. A 45° slope is 100% grade, not 45%. This surprises many people — the chart below makes the non-linear relationship clear.
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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