What this calculator does
Slope percentage expresses how steep a surface is as rise divided by run, multiplied by 100. It is the standard way building codes, accessibility guidelines and civil engineering drawings describe grade, because it is easy to measure on site with just a height and a horizontal distance.
The question of how to calculate ramp slope percentage comes up constantly in accessibility planning, where a maximum allowable grade (commonly 1:12, or about 8.33%) governs how long a ramp needs to be for a given rise. The same calculation applies just as well to a driveway, a drainage pipe fall or any other general grade, not just ramps.
The formula
Slope percentage is the rise divided by the run, multiplied by 100. The same rise and run also give an angle in degrees using the arctangent of rise over run, and a rise-to-run ratio (such as 1:12) that some codes and drawings prefer to a percentage.
| Term | Meaning |
|---|---|
| Rise | The vertical height gained or lost over the length being measured. |
| Run | The horizontal distance over which that rise occurs. |
| Slope percentage | Rise divided by run, expressed as a percentage: (rise ÷ run) × 100. |
| Angle | The same slope expressed as an angle from horizontal, in degrees. |
The inputs explained
| Field | What to enter |
|---|---|
| Rise (vertical height) (m) | The vertical height change over the section being measured. |
| Run (horizontal distance) (m) | The horizontal distance over which that rise happens. Use the same units for rise and run. |
When to use it
Sizing a wheelchair ramp
Working out how to calculate ramp slope percentage from a planned rise lets you check the result against an accessibility maximum, and work backwards to the minimum run (ramp length) needed to stay under it.
Checking a driveway grade
A steep driveway can scrape low cars or become unsafe in wet weather. Measuring rise and run over its length and converting to a percentage grade is the quickest way to check it against a comfortable or code-permitted maximum.
Reading a civil drawing that gives a percentage grade
Site plans and drainage drawings often specify a fall as a percentage. Converting that back to an actual rise over a known run confirms how much height change to expect on site.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
What slope percentage results from common rise-to-run ratios
A fixed 1 metre run, across a range of rise values, showing the resulting percentage and angle.
| Rise (per 1 m run) | Slope percentage | Angle |
|---|---|---|
| 0.02 m | 2.00% | 1.15° |
| 0.04 m | 4.00% | 2.29° |
| 0.08 m | 8.33% | 4.76° |
| 0.10 m | 10.00% | 5.71° |
| 0.15 m | 15.00% | 8.53° |
| 0.20 m | 20.00% | 11.31° |
Questions
What is a typical maximum slope percentage for a ramp?
A commonly cited accessibility maximum is around 8.33% (a 1:12 ratio), but exact limits depend on the specific building code, ramp length and jurisdiction, so always check the applicable local standard rather than relying on a general figure.
Is slope percentage the same as the angle in degrees?
No. A 100% slope is a 45 degree angle, not 100 degrees, because percentage is rise divided by run while degrees measure the actual angle from horizontal. The two only agree at very shallow slopes, where the two measures nearly coincide.
How is this different from a roof pitch calculator?
Roof pitch calculators are built around roof-specific outputs such as rafter length and true roof area from a plan area. This calculator is a general rise-over-run percentage grade useful for ramps, driveways or any other slope, without the roofing-specific extras.
Does it matter what units I use for rise and run?
No, as long as rise and run are both in the same units (both metres, or both feet, for example), since the units cancel out in the ratio and only the percentage and angle results matter.
For a roofing-specific slope with rafter length and roof area, see the roof pitch calculator. For the gradient and line equation between two coordinate points, see the gradient calculator.