Driveway Slope Calculator
A driveway slope calculator divides rise in feet by run × 100 for percent grade; a 6 in rise over 20 ft is 0.5 ÷ 20 = 2.5%, an angle of about 1.43°.
Driveway slope calculator: rise ÷ run × 100
This driveway slope calculator turns two measurements into a grade. The formula is slope % = (rise in inches ÷ 12) ÷ run in feet × 100, and angle = arctangent(rise in feet ÷ run in feet). Enter the vertical rise in inches and the horizontal run in feet. You get the slope as a percent and as degrees, each to two decimals.
What the two numbers mean
Percent grade is how many feet the driveway climbs for every 100 feet you travel. A 10% drive gains 10 ft over a 100 ft run, or 1.2 inches per foot. Contractors, plans, and codes almost always use percent.
Degrees describe the angle you would see with a protractor. It is easier to picture, but small differences hide behind small numbers: 5° sounds gentle, yet it is close to a 9% grade.
The calculator converts the rise from inches to feet first. Then it divides by the run for the ratio, multiplies by 100 for percent, and uses arctangent for the angle.
Worked examples
- Default: 6 in rise over 20 ft
- Rise in feet: 6 ÷ 12 = 0.5 ft
- Slope: 0.5 ÷ 20 × 100 = 2.50%
- Angle: arctan(0.025) = 1.43°
That is a gentle, well-drained grade.
- Garage above the street: 24 in rise over 40 ft
- Rise: 2 ft
- Slope: 2 ÷ 40 × 100 = 5.00%
- Angle: 2.86°
- Hillside drive: 36 in rise over 30 ft
- Rise: 3 ft
- Slope: 3 ÷ 30 × 100 = 10.00%
- Angle: 5.71°
Slope reference table
| Grade | Angle | Rise per 10 ft of run | Feel |
|---|---|---|---|
| 1% | 0.57° | 1.2 in | Barely visible; minimum many use for drainage |
| 2% | 1.15° | 2.4 in | Typical drainage fall |
| 5% | 2.86° | 6 in | Noticeable but easy |
| 8.33% | 4.76° | 10 in | Same as a 1:12 wheelchair ramp |
| 10% | 5.71° | 12 in | Steep for walking |
| 15% | 8.53° | 18 in | Steep; traction matters in ice |
| 20% | 11.31° | 24 in | Very steep for a driveway |
Rules for steep driveways vary by town. Some places set a maximum grade, require a flatter landing near the street or garage, or ask for heated or grooved surfaces. Check local code for your figures.
How to measure driveway slope
- Pick two points: usually the garage slab edge and the back of the sidewalk or street.
- Measure the horizontal run in feet. On a slope, keep the tape level or use a plan view.
- Measure the rise in inches using a string and line level, a laser level, or survey shots.
- For a drive that changes grade, measure each section separately. The steepest section matters most for cars.
Steep driveways and drainage
On a steep drive, water picks up speed and carries gravel or soil with it. A paved drive above about 10% often benefits from a channel or trench drain at the bottom so water does not reach the garage or the street gutter as a sheet. A gravel drive on a steep grade may need crushed stone with fines, which locks better than rounded stone.
At the top and bottom, flatter landings make parking and walking safer. Where the drive meets the street, keep the change in grade gentle so bumpers do not scrape. Your local road department may set the apron shape.
Common slope mistakes
- Measuring along the surface. The run should be horizontal. On gentle slopes the difference is tiny, but on steep ones it adds up.
- Averaging a broken slope. A drive that is flat for 30 ft, then 18% for 10 ft, averages under 5%, but cars feel the 18% section.
- Ignoring the crown of the street. The street often slopes down to a gutter, which adds a grade change at the apron.
- Draining toward the garage. A drive that falls toward the house needs a trench drain or a regrade.
- Mixing units. Rise goes in inches and run in feet.
Related calculators
For general grade work, the slope calculator and drainage slope calculator use the same math. When you are ready to price the surface, try the asphalt driveway cost calculator or the gravel driveway calculator.
This is a planning estimate. Your local building or road department sets maximum driveway grades and apron requirements; confirm with them before grading.
Frequently asked questions
What is the difference between slope percent and degrees?
Percent grade is rise ÷ run × 100, so a 2.5% slope climbs 2.5 ft over 100 ft. Degrees are the actual angle from level, found with arctangent(rise ÷ run). At driveway steepness the two are close to proportional: 10% is about 5.71°, and 20% is about 11.31°.
How do I measure rise and run on an existing driveway?
Run is the horizontal distance in feet between two points, such as the garage slab and the street edge. Rise is the height difference between them in inches. Stretch a string from the high point, level it with a line level, and measure down to the ground at the low point. A laser level makes long runs easier.
Why does a steep slope need a transition at the street?
A sharp change in grade where the driveway meets the street can catch a car's bumper or underside. Breaking the change into shorter sections with gentler grades, often called a transition or apron, softens the angle. Local road departments often specify apron design.
Is a flatter driveway always better?
No. A drive with no slope holds puddles and can send water toward the garage. Many designers aim for at least 1 to 2% fall away from the house, so water runs toward the street or a drain. The best slope is enough for drainage but not so much that cars scrape or slide.
What is the maximum slope for a driveway?
There is no single national number. Many cities and counties set a maximum residential driveway grade, and some require extra measures above a set percentage. Check local code before you grade, and compare your result with the reference table on this page.
Estimates only. Verify quantities with your supplier before purchasing.