Slope Grade Percent Calculator
The slope grade percent calculator finds the grade of a slope from its rise (vertical change in elevation) and run (horizontal distance). It returns the grade as a percentage, the equivalent angle in degrees, and the rise-to-run ratio. Grade percentage is the standard measure used by civil engineers, road designers, and surveyors for specifying and checking slopes, drainage gradients, ramp inclines, and site grading. Enter the rise and run in any consistent unit (feet, meters, etc.) and the calculator handles all the conversions.
Slope grade formula
Grade (%) = (Rise / Run) * 100
Angle (deg) = arctan(Rise / Run) * (180 / pi)
Slope distance = sqrt(Rise^2 + Run^2)
Grade is dimensionless when rise and run use the same unit. A positive grade indicates an uphill slope; a negative rise gives a downhill grade.
Grade reference values
- 0.5% minimum longitudinal grade is recommended for drainage on paved surfaces.
- 2% is typical cross-slope for road drainage (AASHTO).
- 8.33% (1:12) is the maximum ADA ramp slope for accessibility compliance.
- 6% is the typical maximum interstate highway grade in mountain terrain.
- 100% grade equals a 45-degree angle: rise equals run.
Slope grade percent calculator: frequently asked questions
What is slope grade percent?
Slope grade percent is the ratio of vertical rise to horizontal run, expressed as a percentage. A 10% grade means that for every 100 feet of horizontal distance, the elevation changes by 10 feet. It is the standard measure used in road design, drainage, and site grading.
How is grade different from slope angle?
Grade is expressed as a percentage (rise/run * 100). Slope angle is the arctangent of the ratio (in degrees). A 100% grade equals a 45-degree angle. Grade is used in civil engineering and construction; angle is used in trigonometry and some sports applications.
What is a typical road grade?
Interstate highways in the US are typically limited to 6% grade in mountainous terrain and 3% in flat terrain. Local streets may have grades up to 15-20%. Steep residential driveways often reach 25-30%. AASHTO standards govern maximum grades for federal roads.
What is cross-slope and what grade is required for drainage?
Cross-slope is the transverse grade of a road surface that drains water to the edge. AASHTO recommends a minimum cross-slope of 2% on paved surfaces. ADA compliant ramps must have no more than 8.33% running slope and 2% cross-slope.
How do I convert slope percent to degrees?
Angle (degrees) = arctan(grade percent / 100). For example, a 10% grade = arctan(0.10) = 5.71 degrees. Conversely, degrees to percent: grade = tan(angle in radians) * 100.
Official sources
- USGS: USGS topographic mapping and surveying.
- NOAA National Geodetic Survey: NGS elevation and geodetic standards.
Reviewed by the CalculatorHub team, edited by James Graham, 15 June 2026. See our methodology.