Calculate slope percentage, angle, and elevation change between two points based on horizontal distance and rise.
Last updated: March 2026
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Elevation grade is the measure of steepness between two points, expressed as a percentage or slope ratio. It's critical in construction, grading, and drainage design. Grade percentage represents vertical rise per 100 units of horizontal distance. For example, a 5% grade means 5 feet of rise for every 100 feet of horizontal run, commonly seen on roads, ramps, and drainage channels.
Slope ratio (like 1:20) expresses the same relationship differently: 1 unit of rise for every specified number of run units. Angle in degrees provides another way to describe steepness, useful for structural calculations. ADA accessibility requires slopes no steeper than 1:12 (8.3%), while road grades typically range from 2-6%, and steep hillsides can exceed 25%.
Calculate grade percentage, slope ratio, and angle for a 100 ft horizontal run with 5 ft elevation rise:
Grade is expressed as a percentage (rise per 100 horizontal units), while slope is expressed as a ratio (like 1:20). Both describe steepness; grade is common in road/drainage work, slope is common in landscaping and accessibility standards.
ADA accessibility guidelines specify maximum slope of 1:12 (8.3%). Ramps must have no steeper than 1:12 for wheelchairs. Parking lots and sidewalks typically aim for 2-5% for drainage without being steep.
Use the formula: angle (degrees) = arctan(grade% ÷ 100). For example, 10% grade = arctan(0.10) ≈ 5.71°. Most calculators have the inverse tangent (arctan) function built in.
Grade affects drainage, accessibility, structural stability, and site development. Poor grades cause water pooling; excessive grades create safety hazards. Proper grading prevents erosion, flooding, and accessibility issues.
Most roads slope between 2-6%. Highways average 2-3% for drainage on flat terrain. Mountain roads can reach 12%+, but must stay within safety limits. Parking lots typically aim for 1-2%.
Yes. ADA specifies 1:12 max. A 36" rise requires at least 36' of horizontal run. Ramps steeper than 1:12 violate accessibility standards. Hand rails required for ramps over 6" rise.
Minimum 2% grade required for surface drainage (swales, channels). Underground pipes need 0.5-1% slope. Flat grades allow water pooling, creating swamps and ice hazards in winter.
Cut grades lower terrain (removing soil), fill grades raise terrain (adding soil). Both must be calculated separately for earthwork. Fill settles over time; accounting for settlement prevents future grading issues.
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