Slope Percentage Calculator
Convert a slope between percent grade, degrees and ratio, for ramps, roads, paths, drainage and landscaping.
- Degrees
- 4.76°
- Ratio
- 1 : 12
- Rise per 12
- 1/12
- Rise per 100
- 8.33
Accessibility check
Maximum slopes in the 2010 ADA Standards for Accessible Design. Each ramp run may also rise no more than 30 inches before a landing.
| Surface | Maximum | This slope |
|---|---|---|
| Ramp running slopeSection 405.2 | 1:12 (8.33%) | ✓ Within the limit |
| Walking surface running slope (steeper counts as a ramp)Section 403.3 | 1:20 (5%) | ✗ Too steep |
| Cross slope of walks and rampsSection 403.3, 405.3 | 1:48 (2.08%) | ✗ Too steep |
Percent to degrees chart
| Percent | Degrees | Ratio |
|---|---|---|
| 1% | 0.57° | 1 : 100 |
| 2% | 1.15° | 1 : 50 |
| 2.08% | 1.19° | 1 : 48.08 |
| 5% | 2.86° | 1 : 20 |
| 8.33% | 4.76° | 1 : 12 |
| 10% | 5.71° | 1 : 10 |
| 15% | 8.53° | 1 : 6.67 |
| 20% | 11.31° | 1 : 5 |
| 25% | 14.04° | 1 : 4 |
| 33.3% | 18.42° | 1 : 3 |
| 50% | 26.57° | 1 : 2 |
| 75% | 36.87° | 1 : 1.33 |
| 100% | 45° | 1 : 1 |
| 150% | 56.31° | 1 : 0.67 |
| 200% | 63.43° | 1 : 0.5 |
Working out a roof? The roof pitch calculator adds rafter length and roof area. For the slope of a line between two points, use the slope calculator.
Percent, degrees and ratio describe the same slope
Percent grade is rise ÷ run × 100: how many units the surface climbs for every 100 units across. It is how roads, railways, paths and drainage are specified. Theangle is the arctangent of rise ÷ run, and the ratio writes the same thing as 1 : n, the run needed for one unit of rise, which is how ramp and walkway codes state their limits.
Percent and degrees are not proportional. Small slopes are close to linear, so 10% is about 5.7°, but the gap widens fast: 100% is 45°, not 90°, and a vertical face has no percentage at all. Always use the run measured level, not the length along the slope; on gentle slopes the difference is small, on steep ones it is not.
For accessibility, the ADA limit of 1:12 (8.33%) is a maximum, not a target. Gentler ramps are easier to use, and anything steeper than 1:20 (5%) is legally a ramp, which brings landing and edge-protection rules with it, plus handrails once a run rises more than 6 inches. Check local building codes, which can be stricter, before you build.
Frequently asked questions
How do you calculate slope percentage?
Divide the rise by the run and multiply by 100. A path that climbs 3 feet over 60 feet of horizontal distance is 3 ÷ 60 × 100 = 5%. Rise and run must be in the same unit, and the run is the horizontal distance, not the length along the slope.
How do I convert slope percentage to degrees?
Take the arctangent of the percentage divided by 100: degrees = arctan(percent ÷ 100). A 10% grade is arctan(0.1) = 5.71°, and a 50% grade is 26.57°. To go the other way, percent = tan(degrees) × 100.
Is a 100% slope vertical?
No. A 100% slope rises as much as it runs, which is 45°. Percent grade keeps growing past 100% as a slope steepens: 200% is about 63.4°, and a vertical wall would be infinite, because its run is zero.
What is the maximum slope for a wheelchair ramp?
Under the 2010 ADA Standards, a ramp run can be no steeper than 1:12 (8.33%), and no single run may rise more than 30 inches before a level landing. The cross slope, side to side, is limited to 1:48 (about 2.08%). A walking surface steeper than 1:20 (5%) counts as a ramp and must meet the ramp rules. Existing buildings with limited space have some exceptions, and local codes can be stricter.
What does a slope ratio like 1:12 mean?
One unit of rise for every 12 units of horizontal run, whatever the unit. As a percentage that is 1 ÷ 12 × 100 = 8.33%, and as an angle about 4.76°. Roofers write the same idea the other way up, as inches of rise per 12 inches of run, such as 4/12.