Reference
Slope conversion chart.
Percent grade, degrees, ratio, fall per foot and roof pitch, cross-referenced. Every figure computed rather than transcribed, and the page prints cleanly.
Need a single value rather than a table? The slope to degrees converter does any one of these instantly.
Degrees to Percent Grade
Start here when you have measured an angle with a level or an inclinometer.
| Degrees | Percent Grade | Ratio | Fall per Foot (in) |
|---|---|---|---|
| 0.5° | 0.87% | 1 : 114.59 | 0.105″ |
| 1.0° | 1.75% | 1 : 57.29 | 0.209″ |
| 1.5° | 2.62% | 1 : 38.19 | 0.314″ |
| 2.0° | 3.49% | 1 : 28.64 | 0.419″ |
| 2.5° | 4.37% | 1 : 22.9 | 0.524″ |
| 3.0° | 5.24% | 1 : 19.08 | 0.629″ |
| 4.0° | 6.99% | 1 : 14.3 | 0.839″ |
| 5.0° | 8.75% | 1 : 11.43 | 1.050″ |
| 6.0° | 10.51% | 1 : 9.51 | 1.261″ |
| 7.0° | 12.28% | 1 : 8.14 | 1.473″ |
| 8.0° | 14.05% | 1 : 7.12 | 1.686″ |
| 9.0° | 15.84% | 1 : 6.31 | 1.901″ |
| 10.0° | 17.63% | 1 : 5.67 | 2.116″ |
| 12.0° | 21.26% | 1 : 4.7 | 2.551″ |
| 15.0° | 26.79% | 1 : 3.73 | 3.215″ |
| 18.0° | 32.49% | 1 : 3.08 | 3.899″ |
| 20.0° | 36.40% | 1 : 2.75 | 4.368″ |
| 25.0° | 46.63% | 1 : 2.14 | 5.596″ |
| 30.0° | 57.74% | 1 : 1.73 | 6.928″ |
| 35.0° | 70.02% | 1 : 1.43 | 8.402″ |
| 40.0° | 83.91% | 1 : 1.19 | 10.069″ |
| 45.0° | 100.00% | 1 : 1 | 12.000″ |
| 50.0° | 119.18% | 1 : 0.84 | 14.301″ |
| 60.0° | 173.21% | 1 : 0.58 | 20.785″ |
| 75.0° | 373.21% | 1 : 0.27 | 44.785″ |
Ratio to Percent and Degrees
Ratios are how accessibility, drainage and rail work is specified. Remember that a larger second number means a gentler slope.
| Ratio | Percent Grade | Degrees | Fall per Foot (in) | Note |
|---|---|---|---|---|
| 1 : 4 | 25.00% | 14.04° | 3.000″ | — |
| 1 : 6 | 16.67% | 9.46° | 2.000″ | — |
| 1 : 8 | 12.50% | 7.13° | 1.500″ | — |
| 1 : 10 | 10.00% | 5.71° | 1.200″ | — |
| 1 : 12 | 8.33% | 4.76° | 1.000″ | ADA ramp maximum |
| 1 : 14 | 7.14% | 4.09° | 0.857″ | — |
| 1 : 16 | 6.25% | 3.58° | 0.750″ | — |
| 1 : 20 | 5.00% | 2.86° | 0.600″ | Walkway — no ramp handrails required |
| 1 : 24 | 4.17% | 2.39° | 0.500″ | — |
| 1 : 30 | 3.33% | 1.91° | 0.400″ | — |
| 1 : 40 | 2.50% | 1.43° | 0.300″ | — |
| 1 : 48 | 2.08% | 1.19° | 0.250″ | ADA maximum cross slope |
| 1 : 50 | 2.00% | 1.15° | 0.240″ | — |
| 1 : 80 | 1.25% | 0.72° | 0.150″ | — |
| 1 : 100 | 1.00% | 0.57° | 0.120″ | — |
Roof Pitch to Degrees
Roofing uses rise per twelve units of run. For rafter lengths and area factors, use the roof pitch calculator.
| Pitch | Degrees | Percent Grade |
|---|---|---|
| 1/12 | 4.76° | 8.3% |
| 2/12 | 9.46° | 16.7% |
| 3/12 | 14.04° | 25.0% |
| 4/12 | 18.43° | 33.3% |
| 5/12 | 22.62° | 41.7% |
| 6/12 | 26.57° | 50.0% |
| 7/12 | 30.26° | 58.3% |
| 8/12 | 33.69° | 66.7% |
| 9/12 | 36.87° | 75.0% |
| 10/12 | 39.81° | 83.3% |
| 12/12 | 45.00° | 100.0% |
| 15/12 | 51.34° | 125.0% |
| 18/12 | 56.31° | 150.0% |
| 24/12 | 63.43° | 200.0% |
Using the Chart
All four columns describe the same physical steepness. Which one you use is a matter of trade convention rather than accuracy:
- Degrees — anything measured with a level, and most engineering work.
- Percent grade — roads, driveways, earthworks and site drainage.
- Ratio — accessibility, drainage design and rail.
- Fall per foot — plumbing and pipework.
- Pitch — roofing, and nothing else.
The Conversions
grade % = (rise ÷ run) × 100
degrees = arctan(rise ÷ run)
ratio 1 : N where N = run ÷ rise
fall per foot = (grade ÷ 100) × 12 inches
pitch = (grade ÷ 100) × 12
Note that fall per foot and roof pitch use the same arithmetic — both express the rise over twelve units of run. The only difference is that plumbing states it in inches of drop and roofing states it as a dimensionless pitch.
Worth Memorising
- 45° = 100% grade = 12/12 pitch = 1:1. The anchor point for everything else.
- 1:12 = 8.33% = 4.76°. The ADA ramp maximum.
- ¼″ per foot = 2.08% = 1.19°. The usual minimum drain fall.
- 4/12 pitch = 33.3% = 18.43°. A common residential roof.
Knowing those four gives you a sense of scale for almost any slope you meet. Everything else can be estimated by interpolating between them — and checked properly with the slope to degrees converter.
Common Questions
How do I convert percent slope to degrees?
Take the inverse tangent of the grade divided by 100: degrees = arctan(grade ÷ 100). A 25% grade is arctan(0.25) = 14.04°. The relationship is not linear, so a conversion table or a calculator is more reliable than estimating.
What is a 1 in 20 slope as a percentage?
5%. A 1:20 ratio means one unit of rise for twenty of run, and 1 ÷ 20 = 0.05, which is 5%. In degrees it is 2.86°. Under the ADA, a running slope of 1:20 or gentler is treated as a walkway rather than a ramp.
How many degrees is a 2% slope?
1.15°. A 2% grade is very close to the ¼ inch per foot fall used as the minimum for small drain lines, which is 2.08% or 1.19°.
What angle is a 1:12 ramp?
4.76°, which is an 8.33% grade. This is the maximum running slope the 2010 ADA Standards allow for a ramp on an accessible route.
Can I print this chart?
Yes. The page is styled for printing, so the tables come out clean with no navigation, and the reference notes are preserved. It is free to use and no attribution is required.