Percent Grade Calculator
Find site or road grade from elevation change and horizontal distance. Results include percent grade, 1:X ratio, and fall per 100 feet.
Enter your values, then press Calculate.
How to calculate
Enter the elevation difference (rise) and the horizontal run. Field shots are often in feet of rise over a taped distance. The calculator converts both values to feet, then reports percent, ratio, and fall per 100 feet.
Formula
Grade = rise ÷ run. Percent grade = grade × 100. Ratio 1:X uses X = run ÷ rise. Feet per 100 feet equals the percent grade when rise and run use the same length unit.
Common use cases
- Driveway and parking grade checks
- Swale and ditch slopes
- ADA and plan-minimum grade reviews
- Converting 1/4 in per foot to percent
Assumptions
- Rise and run are on the same alignment and the same datum.
- Run is horizontal distance, not slope distance along the surface.
- Percent grade = (rise ÷ run) × 100. A 4 ft rise in 100 ft is 4%.
- Positive rise is uphill in the direction you measured.
Limitations
- Does not output inches per foot. That framing lives on the pipe slope page.
- Does not apply ADA, AASHTO, or driveway-code maximums.
- Does not convert a slope distance from a tape on the hill unless you first reduce it to horizontal.
- Does not compute cut/fill volume from the grade.
Worked examples
4 feet in 100 feet is 4 percent
This is the definition check: 4 ÷ 100 × 100 = 4%. Same rise in 50 ft would be 8%.
1. Decimal slope
4 ft ÷ 100 ft = 0.04 ft/ft
2. Percent grade
0.04 × 100 = 4 %
Quarter inch per foot
1. Decimal slope
0.0208 ft ÷ 1 ft = 0.0208 ft/ft
2. Percent grade
0.020833 × 100 = 2.0833 %
Site and road grade, not pipe inches-per-foot
Percent grade = (rise ÷ run) × 100. A 4 ft rise in 100 ft is 4%. The 1:X ratio is run ÷ rise (4% is 1:25). Feet per 100 feet equals the percent when both inputs use the same length unit. This framing matches driveway, parking, and swale callouts. Utility laterals that are specified in inches per foot belong on the pipe slope page, which uses the same ratio but reports in/ft as a primary field measure.
Common field conversions
1/4 in per foot is 0.25 in rise over 1 ft run = 2.083% (the bundled example). 1/8 in per foot is 1.042%. A 6 in drop across a 50 ft parking aisle is 1%. ADA and plan-minimum grades are design limits, not outputs of this calculator; compare the result to the drawing rather than treating percent grade as a code check.
Driveways, swales, and why 8 percent feels steep
A 4 ft rise in 100 ft is 4% — a comfortable access road. The same 4 ft in 50 ft is 8%, which many residential driveways hit and which starts to bother passenger cars in ice. Enter the rise you leveled and the horizontal run from stationing or a tape reduced to horizontal. If all you have is a slope shot along the pavement, that length is longer than the run and will understate percent grade.
Related calculators
FAQ
What is a 2% grade?
A 2% grade rises or falls 2 feet in 100 feet, or 1/4 inch per foot.
How is this different from pipe slope?
The rise/run math is the same. This page is for roads, drives, pads, and swales and reports percent, 1:X, and feet per 100 feet. Use the pipe slope calculator when the run is a sewer, storm, or other utility and you need inches per foot.
Is run horizontal or slope distance?
Use horizontal run unless the plans explicitly give slope distance. A taped slope on a steep driveway is longer than the station run and will understate percent grade.
How do I get rise if I only have two elevations?
Open the elevation-difference calculator first. Bring that signed difference here as rise, with the horizontal run from stationing or a tape.
Disclaimer
These calculators are estimating tools for planning and field checks. They are not a substitute for approved plans, specifications, licensed professional engineering, or governing standards. Confirm densities, waste factors, and yields with your supplier and project documents.