What is the slope (percent grade)?
Enter the vertical rise and the horizontal run and get the slope instantly — as a percent grade, an angle in degrees and a ratio (1 in n), plus the true length measured along the slope. For example, a rise of 1 over a run of 12 is a 8.33% grade, which is 4.76° or 1 in 12 — the classic ramp slope.
A rise of 1 ft over a run of 12 ft is a 8.33% grade — that is 4.76°, or a ratio of 1 in 12. Measured along the slope, the surface itself is 12.04 ft long.
Percent grade = (rise ÷ run) × 100; angle = atan(rise ÷ run); ratio = 1 in (run ÷ rise); slope length = √(rise² + run²). Percent, angle and ratio are the same in any unit — only the slope length carries a unit. This is pure geometry, not a code value or a product spec.
Slope conversion table
The same steepness written three ways — percent grade, angle and ratio — worked out from atan(rise ÷ run). Your own numbers go into the calculator for an exact figure.
| Percent grade | Angle | Ratio |
|---|---|---|
| 1% | 0.57° | 1 in 100 |
| 2% | 1.15° | 1 in 50 |
| 5% | 2.86° | 1 in 20 |
| 8.33% | 4.76° | 1 in 12 |
| 10% | 5.71° | 1 in 10 |
| 12.5% | 7.13° | 1 in 8 |
| 20% | 11.31° | 1 in 5 |
| 25% | 14.04° | 1 in 4 |
| 33.3% | 18.43° | 1 in 3 |
| 50% | 26.57° | 1 in 2 |
| 100% | 45.00° | 1 in 1 |
Common questions
- How do you calculate slope or grade?
- Divide the vertical rise by the horizontal run and multiply by 100 for the percent grade: grade = (rise ÷ run) × 100. A rise of 1 over a run of 12 is 1 ÷ 12 × 100 = 8.33%. For the angle, take the inverse tangent (atan) of rise ÷ run — atan(1 ÷ 12) = 4.76°. The calculator above does both at once and also gives the ratio.
- What is the difference between percent grade, degrees and a ratio?
- They are three ways to write the same steepness. Percent is rise ÷ run × 100 (used on road signs and in civil works). Degrees is the angle the surface makes with level, atan(rise ÷ run) (used by carpenters and surveyors). A ratio "1 in n" is run ÷ rise (used for ramps and drainage falls). They are not interchangeable numbers — 8.33%, 4.76° and 1 in 12 all describe the very same slope.
- What is a 1:12 slope in percent and degrees?
- A 1:12 slope — 1 unit of rise for every 12 of run — is 8.33% and 4.76°. It is the maximum slope commonly specified for a wheelchair ramp (for example under the ADA in the US), but the exact limit depends on the rules for your project and location, so always check the requirement that applies to you.
- How do I convert percent grade to degrees?
- Take the inverse tangent of the percent divided by 100: degrees = atan(percent ÷ 100). So 5% is atan(0.05) = 2.86°, 10% is atan(0.10) = 5.71°, and 100% (a 1-in-1 slope) is atan(1) = 45°. A 100% slope is not vertical — it is a 45° angle, because rise equals run. To go the other way, degrees to percent, use percent = tan(degrees) × 100.
- What can I use a slope calculator for?
- Any incline where you know two of the three measurements: wheelchair and vehicle ramps, driveway and path gradients, drainage and pipe falls, land grading and cut-and-fill, road and rail grades, conveyor inclines, and stair and handrail pitches. Enter the rise and run and you get the percent, the angle, the ratio and the true length along the slope in one go.
Want the full walk-through? Read the slope guide → Working on a roof? Try the roof pitch calculator →
Reference & education only. Not professional, engineering, or code-compliance advice. Estimates are based on published model codes; local amendments and your Authority Having Jurisdiction (AHJ) govern. Always verify against the current adopted code and a licensed professional before doing work.
Last reviewed 2026-07.