Elevation Grade Calculator
A driveway that rises 2 feet over 40 feet runs at a 5.0% grade, about a 1:20 slope, and a 2.9 degree angle. This elevation grade calculator converts rise and run into the three slope formats people use most for site layout, drainage checks, and driveway planning. Enter the vertical change and horizontal run in the same unit, and the result updates as percent grade, slope ratio, and angle.
Quick answer
Percent grade equals rise divided by run, multiplied by 100.
What this tells you
- •Percent grade equals rise divided by run, multiplied by 100.
- •A 1:20 slope is the same steepness as a 5.0% grade and a 2.9 degree angle.
- •Use horizontal run, not the sloped pavement or ground distance.
- •Keep rise and run in the same unit before you calculate.
How to Use
- 1Measure the vertical change over the stretch you want to check.
- 2Measure the horizontal run over the same stretch.
- 3Enter both numbers in the same unit, such as feet and feet or inches and inches. If the slope falls instead of rises, enter the fall as a positive change amount.
- 4Calculate to see the percent grade, slope ratio, and angle.
- 5Use the result as a layout check, then compare it against the project plan or local requirements.
How It Works
Formula
Percent Grade = (Rise / Run) x 100
Slope Ratio = 1 : (Run / Rise)
Angle = atan(Rise / Run) x 180 / piAll three outputs come from the same rise-to-run fraction. Multiply the fraction by 100 for percent grade. Divide run by rise for the 1:X ratio. Pass the fraction through arctangent to convert it into degrees.
Calculation note: values are processed in the order shown above, using the current input units.
Worked Examples
2 feet of rise over 40 feet of run
Divide 2 by 40 to get 0.05, then multiply by 100 for a 5.0% grade. The same slope reads as 1:20 because 40 divided by 2 is 20.
1 foot of rise over 12 feet of run
This is a common reference slope. The percent grade is 1/12 x 100 = 8.3%, and the angle is about 4.8 degrees.
3 feet of rise over 24 feet of run
Shorter run for the same rise makes the grade steeper. Here the site climbs 1 unit for every 8 units of horizontal travel.
Common Grade Reference Points
Quick slope conversions for site and driveway planning.
| Slope Ratio | Percent Grade | Angle | Typical read |
|---|---|---|---|
| 1:40 | 2.5% | 1.4° | Light yard fall |
| 1:20 | 5.0% | 2.9° | Moderate site grade |
| 1:12 | 8.3% | 4.8° | Noticeably steep |
| 1:10 | 10.0% | 5.7° | Steep driveway |
| 1:8 | 12.5% | 7.1° | Very steep approach |
These reference points describe geometry only. They do not replace project drawings, drainage design, or local code review.
How to Read an Elevation Grade
Percent grade tells you how much vertical change happens over 100 matching units of horizontal run. A 5% grade means 5 units of rise for every 100 units of run, or 1 unit of rise for every 20 units of run.
Slope ratio is often easier to picture in the field because it reads as 1:X. Angle is useful when you are checking equipment specs, ramps, or cut and fill sketches that call out degrees.
For driveways and site work, this calculator is a first-pass geometry check. Surface traction, drainage paths, transitions at the street or garage, and local requirements can still change what is practical to build.
Common mistakes
- Mixing units, such as entering rise in inches and run in feet
- Using the sloped driveway or ground distance instead of horizontal run
- Reading 5% grade as 1:5 instead of 1:20
- Assuming the geometry result alone settles drainage, traction, or permit questions