Slope Percent Grade Calculator
The slope percent grade calculator turns a vertical rise and a horizontal run into a grade expressed as a percentage, the way roads, drainage plans and accessibility standards usually describe steepness. The method is the standard rise-over-run relationship: divide the vertical rise by the horizontal run and multiply by 100. A grade of 5 percent means the ground climbs 5 feet for every 100 feet of horizontal distance. The run is the flat map distance, not the distance measured along the sloping surface, and rise and run must share the same units so they cancel cleanly. Percent grade is not the same as the slope angle in degrees: a 100 percent grade is a 45 degree angle, because at 45 degrees the rise equals the run. Enter your own rise and run to check a driveway against a maximum grade, size a drainage fall, or confirm a ramp meets an accessibility limit. Every figure here is computed deterministically from the formula shown in full below, with a worked example that reconciles exactly to the calculator so you can follow each step and trust the result, and a companion table of common grades for quick reference.
Percent grade equals the rise divided by the run, times 100: grade = (rise / run) x 100. A rise of 5 over a run of 100 is a 5.00% grade. A 100 percent grade equals a 45 degree slope.
Percent grade formula
Grade (%) = (rise / run) x 100
rise = vertical change in height
run = horizontal distance (not slope distance)
The ratio of rise to run measures steepness. Multiplying by 100 expresses it as a percentage, so a rise equal to one hundredth of the run is a 1 percent grade. Rise and run must use the same units.
Worked example
A path rises 5 feet over a horizontal distance of 100 feet.
- Rise = 5, run = 100
- Ratio = 5 / 100 = 0.05
- Grade = 0.05 x 100 = 5%
The grade is 5.00 percent. These are the calculator's default inputs, so the result above matches the widget exactly.
Common grades
Percent grade for a range of rise-over-run ratios.
| Rise | Run | Grade (%) |
|---|---|---|
| 1 | 100 | 1.00 |
| 5 | 100 | 5.00 |
| 8 | 100 | 8.00 |
| 100 | 100 | 100.00 |
Survey and geodetic standards: US National Geodetic Survey (NOAA).
Slope percent grade calculator: frequently asked questions
What is percent grade?
Percent grade is the steepness of a slope expressed as the vertical rise divided by the horizontal run, multiplied by 100. A grade of 5 percent means the ground rises 5 feet for every 100 feet travelled horizontally. Road signs, drainage plans and accessibility standards commonly express slope as a percent grade.
How do I calculate percent grade?
Divide the vertical rise by the horizontal run, then multiply by 100. If the ground rises 5 feet over a horizontal distance of 100 feet, the grade is 5 divided by 100, times 100, which equals 5 percent. Rise and run must use the same units, and run is the horizontal distance, not the distance along the slope.
Is percent grade the same as the slope angle?
No. Percent grade is rise over run as a percentage, while the slope angle is the angle in degrees whose tangent equals rise over run. A 100 percent grade is a 45 degree angle, not 90 degrees, because at 45 degrees the rise equals the run. Use the slope angle calculator to convert a grade into degrees.
What does a 100 percent grade mean?
A 100 percent grade means the rise equals the run: the ground gains 1 foot of height for every 1 foot of horizontal distance. That corresponds to a 45 degree angle, which is very steep. Most roads stay well below 10 percent, and accessibility ramps are typically capped near 8 percent or lower.
Should I use horizontal run or slope distance?
Use the horizontal run, the flat map distance, not the distance measured along the sloping surface. Percent grade is defined as rise over horizontal run. If you only have the slope distance, you can find the horizontal run with the Pythagorean theorem once you know the rise, then apply the grade formula.
Official sources
- Survey, leveling and geodetic standards: US National Geodetic Survey (NOAA). As at 25 June 2026.
Reviewed by the CalculatorHub team, edited by James Graham, 25 June 2026. See our methodology. This is general information, not financial, tax, legal or investment advice.