Convert any slope angle in degrees to a percent grade or a rise-over-12 pitch ratio with the calculator below. Slope percent equals the tangent of the angle multiplied by 100; the rise per 12 of run equals 12 times the tangent of the angle. Both values appear instantly as you change the angle.
The same tool serves several jobs depending on what you call it. As a slope percentage calculator, it returns the percent-grade equivalent of any angle. As a slope degrees to percent calculator, it converts directly between the two unit systems. As a degree to slope percentage tool, it accepts an angle and returns the percent. As a grading slope calculator, it works for site grading, driveways, and parking-lot drainage where percent grade is the standard. The same calculator handles slope percentage queries (e.g., "what percent slope is 15 degrees?") and reverse queries (e.g., "what angle gives me a 1/4 slope?" — answer: 14 degrees).
Use this conversion for roof pitch (where rise/12 is the convention), road and driveway grades (where percent is the convention — including specific reference angles like 15 degree slope and 12 degree grade common in road and driveway design), and any application that needs to translate between the two formats.
The conversion formula
Slope percent = tan(angle) × 100. A 30° angle gives tan(30°) × 100 ≈ 57.7% slope. A 45° angle gives tan(45°) × 100 = 100%, because the tangent of 45° is exactly 1.
Going the other direction: angle in degrees = arctan(percent ÷ 100), converted from radians to degrees by multiplying by 180/π. A 50% grade becomes arctan(0.5) × 57.296 ≈ 26.57°, which is also a 6/12 roof pitch.
Common conversions worth memorising
1° ≈ 1.75% slope. 5° ≈ 8.75%. 10° ≈ 17.6%. 15° ≈ 26.8%. 20° ≈ 36.4%. 30° ≈ 57.7%. 45° = 100%. 60° ≈ 173%.
For roof pitch reference: 4.76° = 1/12 (8.3%), 14.04° = 3/12 (25%), 18.43° = 4/12 (33.3%), 26.57° = 6/12 (50%), 33.69° = 8/12 (66.7%), 45° = 12/12 (100%).
| Angle (degrees) | Percent slope | Rise / 12 pitch | Common application |
|---|---|---|---|
| 1° | 1.75% | 0.21 / 12 | Drainage minimum on flat roofs |
| 2° | 3.49% | 0.42 / 12 | Standard low-slope drain to scupper |
| 4.76° | 8.33% | 1 / 12 | ADA-compliant ramp max; flat roof transition |
| 7° | 12.28% | 1.47 / 12 | 12% driveway / road grade limit (residential) |
| 9.46° | 16.67% | 2 / 12 | Asphalt-shingle minimum (with sealed underlayment) |
| 14.04° | 25% | 3 / 12 | Sheds, garages, mainstream metal-panel minimum |
| 15° | 26.79% | 3.22 / 12 | Common surveyor / road slope reference |
| 18.43° | 33.33% | 4 / 12 | IRC steep-slope threshold; common residential pitch |
| 22.62° | 41.67% | 5 / 12 | Conventional residential |
| 26.57° | 50% | 6 / 12 | Versatile mid-pitch; "comfortable" residential |
| 30° | 57.74% | 6.93 / 12 | Boundary for walkable roof; mid-steep residential |
| 33.69° | 66.67% | 8 / 12 | Steep residential; walkability threshold |
| 39.81° | 83.33% | 10 / 12 | Steep traditional styles (Victorian, Tudor) |
| 45° | 100% | 12 / 12 | Equal rise and run; common in attic conversions |
| 56.31° | 150% | 18 / 12 | Very steep; specialty / aesthetic |
| 60° | 173.21% | 20.78 / 12 | Mansard-style upper sections |
| 63.43° | 200% | 24 / 12 | Tower-style / accent dormers |
When you need this conversion
Drainage design — civil engineers spec slopes in percent (e.g., "minimum 2% slope to drain"), but field staff often think in rise/run. The conversion lets both sides speak the same language.
Driveway grade compliance — most municipal codes cap residential driveways at 12–15%. A surveyor reports the angle in degrees; you need percent for the permit.
Solar panel optimization — solar racking specs typically use degrees, but if your roofer talks in rise/12, the conversion lets you confirm the panel angle matches the roof pitch.
Need to run the numbers?Use the free roof pitch calculator on the home page to convert pitch to angle, calculate rafter length, or estimate roof area in any unit.