Grade Calculator: Free Online Slope & Elevation Calculator
Use our free grade calculator to compute slope percentages, ratios, and elevation differences for any land grading, road design, or drainage project. Designed for civil engineers, landscapers, and site contractors, this tool calculates grade from elevation change and horizontal distance. Enter your rise and run values to get instant results in percentage, ratio, and angle formats.
How to use this calculator.
- Enter the elevation change (rise). Input the vertical distance between your start and end points, in feet or meters. This can be positive (uphill) or negative (downhill).
- Enter the horizontal distance (run). Input the horizontal length of the slope, measured along the ground in the same unit system.
- Select your preferred output format. Choose from grade percentage (%), slope ratio (e.g., 4:1), or angle in degrees depending on your project requirements.
- Click Calculate. The tool instantly computes the grade in all standard formats so you can verify plans or set up grading equipment.
- Check against standards. Compare your result against applicable codes for roadways, ADA ramps, or drainage slopes.
How do you calculate slope grade, rise, run, and ratio?
Grade is the measure of steepness of a slope, expressed as a percentage, ratio, or angle. The three common representations are calculated from the same rise and run values.
Grade (%) = (Rise ÷ Run) × 100
Slope Ratio = Run : Rise (typically reduced so rise = 1)
Angle (°) = arctan(Rise ÷ Run)
Where:
- Rise: The vertical change in elevation, typically in feet or meters.
- Run: The horizontal distance over which the elevation change occurs, in the same unit as rise.
- Grade percentage: A 5% grade means the elevation changes 5 feet for every 100 feet of horizontal distance.
Example calculation.
Let's calculate the grade for a driveway approach.
Scenario: Your driveway rises 4 feet in elevation over a horizontal distance of 50 feet from the street to the garage.
- Identify rise and run: Rise = 4 ft, Run = 50 ft
- Calculate grade percentage: (4 ÷ 50) × 100 = 8.0%
- Calculate slope ratio: 50 ÷ 4 = 12.5 : 1, so the slope is approximately 12.5:1.
- Calculate angle: arctan(4 ÷ 50) = arctan(0.08) = 4.57°
Result: The driveway has an 8% grade(approximately 12.5:1 slope). This is within the typical residential driveway maximum of 10–15%.
Tips from the field.
- ADA ramps require 5% maximum. The Americans with Disabilities Act specifies a maximum running slope of 1:20 (5%) for accessible routes and 1:12 (8.33%) for ramps with landings.
- Roadway maximums vary by classification. Interstate highways typically max at 6%, arterial roads at 8%, and local streets at 12%. Mountain roads may reach 15% with reduced speed limits.
- Minimum slope for drainage is 1–2%. Paved surfaces, swales, and gutters need at least 1% grade to carry water. Standing water accelerates pavement deterioration.
- Use a laser level for accuracy. For precise grade measurement on site, a rotary laser level is far more reliable than a string line over long distances.
- Cross-slope matters too. Roads need 1.5–2% cross-slope (crown) to shed water to the shoulders. Insufficient cross-slope leads to hydroplaning risk.
Disclaimer: This calculator provides estimates for planning purposes only. Actual site grades must be verified by field survey. Roadway, drainage, and accessibility designs must comply with applicable local, state, and federal codes. For engineered grading plans, consult a licensed civil engineer or professional land surveyor. PavementCalculator.com assumes no liability for grading errors or code violations.
Cost, price, and density figures on this page reflect approximate U.S. averages as of August 2026 and vary by region, supplier, and material availability.
Frequently asked questions.
How do I calculate grade percentage?
Grade (%) = (Rise ÷ Run) × 100. For example: a 3-foot rise over 100 feet of run = (3 ÷ 100) × 100 = 3% grade. This means the ground rises 3 feet for every 100 feet of horizontal distance. A 45° slope = 100% grade (rise equals run). For roads, grade is expressed as a percentage, e.g., '6% grade' means 6 feet of rise/loss per 100 feet. Use our calculator above to convert between grade %, angle, and ratio.
What is the minimum slope for drainage?
Minimum drainage slopes: Paved surfaces: 1-2% (1/8-1/4 inch per foot). Unpaved surfaces/grass: 2-5%. Swales: 2-4% minimum longitudinal slope, 1% minimum for lined swales. Underground pipes: 1% minimum for 4-inch, 0.5% minimum for 6-inch and larger (check local codes). Flat roofs: 1/4 inch per foot (2%). The absolute minimum to prevent standing water is 0.5%: anything flatter risks ponding. ADA requires cross-slopes of 1.5-2% maximum for accessible routes.
What is the maximum slope for a driveway?
Residential driveway maximum slope: 12-15% is the practical limit for passenger vehicles. At 15%, a car's bumper may scrape at the transition (where flat garage meets sloped driveway). Commercial driveways: 8-10% maximum. Parking lot aisles: 5-8% maximum. Accessible routes: 5% maximum running slope (1:20), with 8.3% (1:12) maximum for ramps. Transition zones (3-6 feet long) at the top and bottom of steep driveways prevent scraping.
How do I read a grading plan?
Grading plans use contour lines showing existing and proposed elevations. Contour lines connect points of equal elevation. Closely spaced contours = steep slope; widely spaced = gentle slope. Spot elevations marked with an 'x' or '+' show specific points. Existing contours are typically dashed; proposed are solid. Cut areas (where soil is removed) and fill areas (where soil is added) are often color-coded. The difference between existing and proposed contours tells you the cut/fill depth at any point.
What tools do I need for site grading?
Basic grading tools: (1) Transit or laser level: establishes grade elevations. (2) Grade rod/stadia rod: reads elevations. (3) String line and line level: sets straight grade lines between stakes. (4) Grade stakes with markings (cut/fill at each stake in tenths of feet). (5) Hand level or clinometer for quick slope checks. For DIY projects, a string line and a line level can establish a basic grade. Professional grading uses GPS-equipped bulldozers that adjust the blade automatically based on a digital terrain model.
What is a good slope for a residential driveway?
Residential driveways should have a slope between 2% and 10%, with 5–8% being the sweet spot for drainage without scraping vehicle undercarriages. Slopes over 15% may cause vehicles to bottom out and can be hazardous in icy conditions.
How do I convert between grade percentage and ratio?
Divide the run by the rise to get the ratio. For example, a 25% grade (25 feet rise per 100 feet run) is a 4:1 slope (100 ÷ 25 = 4). Use our grade calculator above for instant conversion between all formats.
What is the steepest road grade in the United States?
Canton Avenue in Pittsburgh, Pennsylvania holds the record at 37% grade. For comparison, the steepest residential streets typically range from 25–35% in hilly cities like San Francisco and Pittsburgh.
What does a 2% grade look like?
A 2% grade rises 2 feet for every 100 feet of horizontal distance. It is barely perceptible to walk on but sufficient for drainage. Most parking lots and sidewalks are designed with 1–2% cross-slope minimums.
How is grade used in stormwater management?
Grade determines flow velocity and capacity of drainage swales, pipes, and channels. Manning's equation uses slope as a key input. Too little slope causes ponding; too much causes erosion. Typical drainage swale grades range from 1–5%.