Use this Elevation Grade Calculator to calculate slope ratio, percent grade, angle of elevation, and 1 in N ratio from vertical rise and horizontal run.

Elevation Grade Formulas

Slope = rise ÷ horizontal run

Percent grade = (rise ÷ horizontal run) × 100

Angle = arctan(rise ÷ horizontal run)

1 in N ratio: N = horizontal run ÷ rise

Rise and run must use compatible units. The calculator converts mixed units before calculating.

Example

Suppose the vertical rise is 3 ft and the horizontal run is 24 ft.

Slope = 3 ÷ 24 = 0.125

Percent grade = 0.125 × 100 = 12.5%

Angle = arctan(0.125) ≈ 7.13°

1 in N = 24 ÷ 3 = 8

The slope can therefore be expressed as 0.125, 12.5%, 7.13°, or 1 in 8.

Important Notes

• Use horizontal run, not the distance measured along the sloped surface.
• A negative rise represents a descending slope.
• If the rise is zero, the grade is 0%.
• If the horizontal run is zero, percent grade is undefined.
• For ramps, roads, drainage, driveways, or other regulated work, verify the result against applicable design standards and local requirements.

Sources

• U.S. Geological Survey — Determine Percent Slope and Angle of Slope
• U.S. Access Board — Ramps and Curb Ramps