Elevation Grade Calculator
Find the slope of ground, a driveway or a ramp. Start from rise & run, a known grade, or a known angle plus the run, and get the grade percentage, the angle from level, the slope ratio (run:rise) and the length measured along the slope — with an optional check against common benchmarks (drainage, ADA ramp, driveway), by-grade and benchmark tables, a chart, and a downloadable PDF.
| Grade | Angle | Ratio (run:rise) | Rise over run |
|---|---|---|---|
| Enter a slope to compare | |||
| Use | Grade | Ratio | Angle |
|---|---|---|---|
| Enter a slope to compare | |||
How to use the elevation grade calculator
Four quick steps turn a slope into its grade, angle, ratio and length — starting from rise and run, a known grade, or a known angle, with an optional check against drainage, ramp and driveway benchmarks.
Pick what you know
Rise & run, grade & run, or angle & run.
Enter the values
The vertical rise or grade or angle, plus the horizontal run.
Choose a benchmark
Check against drainage, an ADA ramp or a driveway — or none.
Read results & save a PDF
Get the grade, angle, ratio and slope length — then download a report.
The formulas behind the grade
The grade, angle and ratio all come from the rise and the run; the slope length is the hypotenuse of the two.
▶ Worked example
A 2 ft rise over a 20 ft run.
Grade = 2 ÷ 20 × 100 = 10%; angle = arctan(2 ÷ 20) = 5.71°; ratio = 100 ÷ 10 = 10 : 1.
Slope length = √(2² + 20²) = 20.1 ft — only about an inch longer than the run.
Grade 10% · angle 5.71° · ratio 10:1 · slope length 20.1 ft
That is a comfortable driveway grade, well under the ~15% maximum, but too steep for an ADA ramp (8.33% max).
Elevation grade quick reference
The slope formulas, the angle and ratio for each grade, and common grade benchmarks for drainage, ramps and driveways.
| Quantity | Formula |
|---|---|
| Grade (percent) | rise ÷ run × 100 |
| Angle from level | arctan(rise ÷ run) |
| Slope ratio | 100 ÷ grade, as n : 1 |
| Slope length | √(rise² + run²) |
| Rise from grade | run × grade ÷ 100 |
| Grade from angle | tan(angle) × 100 |
| Grade | Angle | Ratio (run:rise) | Rise over 20 ft |
|---|---|---|---|
| 1% | 0.57° | 100 : 1 | 0.20 ft |
| 2% | 1.15° | 50 : 1 | 0.40 ft |
| 5% | 2.86° | 20 : 1 | 1.00 ft |
| 8.33% | 4.76° | 12 : 1 | 1.67 ft |
| 10% | 5.71° | 10 : 1 | 2.00 ft |
| 15% | 8.53° | 6.7 : 1 | 3.00 ft |
| 20% | 11.31° | 5 : 1 | 4.00 ft |
| 25% | 14.04° | 4 : 1 | 5.00 ft |
| Use | Grade | Angle | Ratio |
|---|---|---|---|
| Drainage minimum (away from house) | 2% | 1.15° | 50 : 1 |
| Gentle slope | 5% | 2.86° | 20 : 1 |
| ADA ramp maximum | 8.33% | 4.76° | 12 : 1 |
| Driveway comfortable | 10% | 5.71° | 10 : 1 |
| Driveway maximum | 15% | 8.53° | 6.7 : 1 |
| Very steep | 25% | 14.04° | 4 : 1 |
Benchmarks are common rules of thumb and vary by jurisdiction and site — drainage ~2% minimum away from a foundation, ADA ramps at 8.33% (1:12) maximum, residential driveways at roughly 15% maximum. Confirm against your local code.
Everything the calculator returns
One calculation gives the full slope picture — every way of expressing it, plus a benchmark check.
Slope at a glance
The common benchmarks, and the default result.
Built for the way you work
Whether you are grading a yard, laying a driveway, or designing an accessible ramp, the slope math starts from the same inputs.
Setting grades for drainage and planting, and need to be sure the ground falls away from the house at a working slope.
- Keep at least 2% away from walls
- Check rise over the real run
- Confirm with a level or laser
Laying out a driveway or path and want to keep it drivable, under the ~15% limit with comfortable transitions.
- Aim for 10% or less
- Watch the top and bottom breaks
- Get the slope length for material
Designing an accessible ramp and need the run for a given rise at the 8.33% (1:12) maximum, with room for landings.
- Hold 1:12 or gentler
- 12 ft of run per foot of rise
- Add landings and handrails
Get the grade right
Seven things that keep a slope estimate honest.
Grade isn’t the angle
A 100% grade is only 45°, not 90°. Percent and degrees diverge fast — read the one your spec actually calls for.
Drain away from the house
Keep at least about 2% fall away from the foundation. Flat or back-pitched ground is the root of most water problems.
ADA ramps are 1:12
8.33% maximum means 12 ft of run for every foot of rise. Gentler is easier — and landings and handrails are still required.
Keep driveways drivable
Hold driveways to about 15% or less, and watch the transitions at the top and bottom so cars don’t scrape.
Run is horizontal
The run is the level distance, not the distance along the ground. Measuring along the slope overstates the run and understates the grade.
Use the slope length for material
Paving, pipe or ramp decking follows the slope, which is a touch longer than the run — order to the slope length.
Measure, don’t eyeball
Slopes are deceptive by eye. A level and tape, a laser or a survey gets rise and run right before you grade or pour.
Frequently asked questions
Common questions about elevation grade, slope ratio, drainage, ramps and driveways.
Elevation grade is the slope of the ground expressed as a percentage: the vertical rise divided by the horizontal run, times 100. The run is the level (map) distance between the two points, not the distance along the slope.
So a grade tells you how many feet of rise you get per 100 feet of run — a 10 percent grade climbs 10 feet over 100 feet. From the same rise and run you also get the angle and the slope ratio.
For example, a rise of 2 feet over a 20 foot run is 2 divided by 20 times 100, which is a 10 percent grade, a 5.71 degree angle and a 10 to 1 ratio. This calculator works all of these out from rise and run, a known grade, or a known angle.
They are three ways of describing the same slope. The grade is the rise over the run as a percentage. The angle is the same slope measured in degrees from level, found as the arctangent of rise over run. The slope ratio expresses it as run to rise, written like 10 to 1.
They do not line up in a simple way: a 100 percent grade is a 45 degree angle and a 1 to 1 ratio, not 90 degrees. A gentle 2 percent grade is only about 1.15 degrees.
For example, a 10 percent grade is a 5.71 degree angle and a 10 to 1 ratio. This calculator reports all three from whichever one you start with, so you can move between them.
For water to drain away from a building, the ground should fall at least about 2 percent — 2 feet of drop over 100 feet — away from the foundation. That is a common minimum; many codes ask for a set drop within the first several feet around the house.
Too little slope and water pools or runs back toward the foundation; a bit more than the minimum is fine and often better. Hard surfaces like patios can sometimes use a little less, but 2 percent is the usual target for soil.
For example, a 2 percent grade is about 1.15 degrees, or a 50 to 1 ratio. This calculator can check your grade against the 2 percent drainage benchmark. Always confirm the required fall with your local code.
An ADA-compliant ramp has a maximum running slope of 8.33 percent, which is a 1 to 12 ratio — one unit of rise for every twelve of run. That works out to about 4.76 degrees.
The 1 to 12 limit means a ramp needs at least 12 feet of run for every foot it climbs, which is why accessible ramps are long and often switch back. Gentler slopes like 1 to 16 or 1 to 20 are easier to use where there is room, and ramps also need level landings and handrails.
For example, an 8.33 percent grade is a 1 to 12 ratio at about 4.76 degrees. This calculator checks your grade against the 8.33 percent ADA ramp maximum. Confirm the full ramp requirements against the ADA and your local code.
Residential driveways are usually kept at or below about 15 percent — 15 feet of rise over 100 feet. Steeper than that and vehicles can scrape, struggle for traction in ice or snow, and the transitions at the top and bottom become hard to drive.
A grade around 10 percent or less is comfortable; up toward 15 percent is the practical maximum, and anything steeper usually needs special transitions, drainage and sometimes a variance. Local codes and the slope of the street also matter.
For example, a 15 percent grade is about 8.53 degrees, a 6.7 to 1 ratio. This calculator checks your grade against the roughly 15 percent driveway maximum. Confirm the limit with your local jurisdiction.
A percent grade and an angle in degrees describe the same slope but are not interchangeable numbers. To convert a grade to an angle, take the arctangent of the grade divided by 100. To go the other way, the grade is the tangent of the angle times 100.
They only match at the extremes you would not expect: a 100 percent grade is 45 degrees, not 100, and a 0 percent grade is 0 degrees. In between, the angle rises more slowly than the grade.
For example, a 10 percent grade is the arctangent of 0.10, about 5.71 degrees; a 15 percent grade is about 8.53 degrees. This calculator shows the grade, the angle and the ratio together so you never have to convert by hand.
The run is the horizontal distance between two points — the level, plan-view distance. The slope length is the distance measured along the sloped surface itself, from the bottom to the top. The slope length is always a little longer than the run, by the Pythagorean theorem: it is the square root of the rise squared plus the run squared.
For gentle grades the two are nearly equal, but they diverge as the slope steepens. The slope length is what you need for the actual material — the ramp surface, the length of pipe or paving along the grade.
For example, a 2 foot rise over a 20 foot run has a slope length of about 20.1 feet — only an inch or so longer. This calculator reports the slope length alongside the grade and angle.
The run is the horizontal distance and the rise is the vertical change between your two points. The cleanest way is with a level or laser: set a level line from the high point, measure horizontally out to the run distance, then measure straight down to the ground for the rise.
For short distances a long level or a straight board with a level on it works; for longer runs or precise work, a laser level, a transit, or a survey is better. Keep the run truly horizontal, or the grade will come out wrong.
Once you have the rise and the run in the same units, this calculator gives the grade, angle, ratio and slope length. For anything you will build or grade to, confirm the elevations with a proper level or survey.
Disclaimer: US units (feet). Grade % = rise ÷ run × 100; angle = arctan(rise ÷ run); slope length = √(rise² + run²); ratio = run ÷ rise. The benchmarks shown — drainage about 2% minimum away from a foundation, an ADA ramp at 8.33% (1:12) maximum, and residential driveways at roughly 15% maximum — are common rules of thumb that vary by jurisdiction and site. A planning aid only — confirm elevations with a level, laser or survey and follow your local code before grading, paving or building a ramp.