Degrees to Percent Slope
Type an angle in degrees to get the slope as a percent and as a 1:n ratio.
Indicative estimate · not a survey or a design · see methodology
Is this the slope of your land? Draw the plot and see the gradient by zone, the sun and what fits.
Open the land plannerTypical slopes and what they mean
| Slope | Degrees | Ratio | Where you meet it |
|---|---|---|---|
| 1 % | 0.6° | 1:100 | Minimum fall for surface drainage on paving |
| 2 % | 1.1° | 1:50 | Patios and paths draining away from a house |
| 5 % | 2.9° | 1:20 | ADA accessible route maximum |
| 8.33 % | 4.8° | 1:12 | ADA ramp maximum |
| 10 % | 5.7° | 1:10 | Comfortable driveway; gentle hillside lot |
| 15 % | 8.5° | 1:6.7 | Typical residential driveway maximum |
| 25 % | 14° | 1:4 | Steep lot: stepped foundations, retaining walls |
| 50 % | 26.6° | 1:2 | Very steep; usually unbuildable without engineering |
| 100 % | 45° | 1:1 | A 45° angle equals 100 %, not 100° |
Source: ADA Standards 2010 §405 (1:12 ramps, 1:20 routes); common US municipal driveway standards · verified 2026-08-22
How slope is calculated
slope % = rise ÷ run × 100 · degrees = atan(rise ÷ run) · ratio = 1 : (run ÷ rise)
A driveway climbs 2 m over 20 m of horizontal distance: 2 ÷ 20 = 0.10 → 10 %. atan(0.10) = 5.7°. Ratio 1:10. If you measured 20 m along the ground instead of horizontally, the run is √(20² − 2²) = 19.9 m and the slope is 10.05 %.
- Rise and run use the same unit; the result is unit-free.
- Degrees and percent are not proportional: 45° is 100 %, 90° is infinite.
- Limits shown are common defaults; your municipality or HOA may set others.
What people use it for
Driveway access
Keep a car driveway under 15 % (12 % with snow) and flatten the last 5 m before the garage so bumpers do not scrape.
Drainage away from the house
Grade the first 3 m from the foundation at 5 % (15 cm drop) and paving at 1–2 % so water leaves.
Choosing a lot
Under 5 % builds on a slab; 5–15 % may need a stepped foundation; over 15 % means engineered footings and retaining — and higher cost per m².
Accessible paths
Routes over 5 % must be designed as ramps with landings; the 1:12 maximum is the number inspectors check.
Frequently asked questions
How do I convert slope percent to degrees?
degrees = atan(percent ÷ 100). A 10 % slope is atan(0.10) = 5.7°; 20 % is 11.3°; 100 % is 45°.
What is a 1:12 slope in percent?
1 unit of rise per 12 of run: 1 ÷ 12 × 100 = 8.33 %. That is the ADA ramp maximum.
Is a 10 % slope steep?
It is moderate. Fine for a driveway and for building with some grading; too steep for an accessible route (5 % max).
What is the maximum slope for a driveway?
Most US guidance caps residential driveways at 15 % (about 8.5°), and 12 % where ice or snow is common. Check your local code.
How do I find the slope of my land?
Measure the elevation difference between two points and the horizontal distance between them, then divide. With an address, the planner reads public elevation data for you.
What does 100 % slope mean?
Rise equals run — a 45° angle. Percent slope goes past 100 % as the angle approaches 90°.
What is a 2 % slope over 10 feet?
10 ft × 0.02 = 0.2 ft, about 2.4 inches of fall — the usual minimum for paving to drain.
How steep is a 30 degree slope?
tan(30°) = 0.577, so 57.7 % — very steep for a site; typically unbuildable without engineering.
Related tools
Sources and author
Terramify editorial team · Research and data verification · Updated August 22, 2026
Source: ADA Standards 2010 §405 (1:12 ramps, 1:20 routes); common US municipal driveway standards
Indicative estimate · not a survey or a design · see methodology