Calculate the slope of an accessible ramp, garage driveway, roof pitch or drainage pipe converting between percentage (%), angle in degrees and vertical rise.
Accessibility & Building Code (ADA / IBC & EN): A 100% slope equals a 45° angle. Accessible pedestrian ramps typically require a maximum slope of 8% (or 1:12 = 8.33% under ADA).
| Building Element | Reference Standard | Required Slope (%) | Angle in Degrees |
|---|---|---|---|
| Accessible ramp (short runs < 3 m) | Accessibility Standard (ADA / EN / CTE) | Max 10 % | 5.71° (10 cm per meter) |
| Accessible ramp (medium runs 3 to 6 m) | Accessibility Standard (ADA / EN / CTE) | Max 8 % (ADA 8.33%) | 4.57° (8 cm per meter) |
| Accessible ramp (long runs > 6 m) | Accessibility Standard (ADA / EN / CTE) | Max 6 % | 3.43° (6 cm per meter) |
| Vehicle garage ramp (straight / curved) | Parking & Garage Code | Max 16%-18% (straight) / 12% (curved) | 9.09° to 10.20° |
| Flat roof / Walkable terrace drainage | Roof Waterproofing Code | 1 % to 5 % | 0.57° to 2.86° |
| Pitched roof with curved clay tiles | Pitched Roof Code (EN / DTU / DIN) | Min 26 % - 32 % | 14.5° to 17.7° |
Divide vertical rise by horizontal run and multiply by 100: Slope (%) = (Rise / Run) × 100. Angle in degrees = arctan(Slope% / 100) × (180 / π).
Under ADA standards (1:12 ratio), maximum ramp slope is 8.33% (4.76°), while European codes require 6% to 8% depending on ramp length.