Enter rise and run — or start from a known percent grade, angle in degrees, or 1-in-N ratio — and the Slope Percentage Calculator converts between all four formats. Your results include slope %, angle (°), ratio (1 in N), and a visual breakdown so you can understand exactly how steep your road, ramp, or terrain really is.
Slope Percentage
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Angle
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Ratio (1 in N)
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Steepness Category
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Divide the rise (vertical change) by the run (horizontal distance) and multiply by 100. The formula is: slope % = (rise / run) × 100. For example, a rise of 5 m over a run of 100 m gives a 5% slope.
Use the arctangent function: angle = atan(slope% / 100). For a 5% slope, angle = atan(0.05) ≈ 2.86°. Note that slope % and degrees are not the same — a 100% slope equals 45°, not 90°.
Yes. A negative slope percentage simply means the terrain goes downhill in the direction of travel. The magnitude of the percentage describes the steepness, while the sign indicates direction.
Absolutely. A 100% slope means rise equals run, which is a 45° angle. Slopes steeper than 45° have a percentage greater than 100%. Very steep mountain roads or ski runs can exceed 100% grade.
A '1 in N' ratio means for every N units of horizontal distance, the elevation changes by 1 unit. It is related to percent grade by the formula: % = 100 / N. For example, a 1-in-20 ratio equals a 5% grade.
Rearranging the formula: run = rise / (slope% / 100) = 1 / 0.05 = 20 m. So the ramp must be 20 m long horizontally to achieve a 1 m rise at 5% grade.
A 5% road grade is considered moderate and is common on highways. Most standard roads stay under 6–8%. Grades above 10% are considered quite steep for road driving, while grades above 20% are rare and challenging.
Rise and run can be in any unit of length — meters, feet, inches, etc. — as long as both use the same unit. Since slope percentage is a ratio, the units cancel out and the result is dimensionless.