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 | Ratio | Application |
|---|---|---|---|
| 1.15° | 2% | 1 in 50 | Minimum road drainage slope |
| 4.76° | 8.33% | 1 in 12 | Maximum ADA wheelchair ramp |
| 5.71° | 10% | 1 in 10 | Steep residential driveway |
| 10.00° | 17.63% | 1 in 5.7 | Challenging cycling climb |
| 26.57° | 50% | 1 in 2 | Very steep terrain |
| 45.00° | 100% | 1 in 1 | Equal rise and run |
The angles here are given to two decimals on purpose. Round 4.76° to 4.8° and the grade it produces is 8.40%, which would fail an 8.33% ADA check on paper even though the ramp is fine. Rounding an angle is not a harmless simplification when the tangent is what gets inspected.
Important Note
Percent grade is NOT the same as angle in degrees. A 45° slope is 100% grade, not 45%. This surprises many people, and it is why the chart below plots both against a single shared axis: the grade curve peels away from the straight angle line almost immediately, and by 45° it is more than double.
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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