Topographic Slope & Grade Calculator
Calculate slope percentage, slope angle in degrees, and grade (rise over run) from elevation change and horizontal distance.
Results
What is it?
Slope is the ratio of vertical rise to horizontal run, expressed as a percentage, decimal fraction, or angle. A 20% slope means for every 100 m horizontal you rise 20 m. In geography and civil engineering, slope percentage is most commonly used; road signs typically show grade percentage.
How to use
Enter the elevation change (read from contour lines on a topographic map ? multiply contour interval by the number of lines crossed) and the horizontal distance between those points. The calculator gives slope percentage, angle, and the fractional gradient.
Example scenario
A hill rises 100 m over 500 m horizontal distance: slope = 20%, angle = 11.3 degrees, grade = 0.20. A road with an 8% grade rises 8 m per 100 m of horizontal travel ? the maximum for most highways in mountainous terrain.
Pro tip
Slopes above 30% are considered steep in hillwalking. Ski runs are graded: green < 25%, blue 25-40%, red 40-60%, black > 60%. In agriculture, slopes > 8% are prone to erosion without terracing. Landslide risk generally increases sharply above 15-20% on unstable soils.