Choose what you want to find, type the other two measurements and see the ramp drawn with the result and whether it meets the ADA accessible ramp rules (US). Other countries have their own codes.
With the rise and the length, we work out the slope of the ramp.
The length is measured on the ground (horizontal projection, the “run”), from the start to the end of the ramp. Accessible ramp (ADA): up to 8.33% (1:12).
Result
ADA limits for accessible ramps (US 2010 Standards, §405)
| Running slope | Ratio | Max. rise per run | Applies to |
|---|---|---|---|
| up to 5% | 1:20 | — (not a ramp) | walking surface: no landings needed |
| 5% to 8.33% | 1:12 | 0.760 m (30 in) | new construction and alterations |
| 8.33% to 10% (existing sites only) | 1:10 | 0.150 m (6 in) | only where space is limited |
| 10% to 12.5% (existing sites only) | 1:8 | 0.075 m (3 in) | only where space is limited |
Every run needs a level landing at the top and at the bottom, at least 1.525 m (60 in) long and as wide as the ramp; where the ramp changes direction the landing must be at least 1.525 × 1.525 m (60 × 60 in). Clear width at least 0.915 m (36 in), cross slope not steeper than 1:48 (2.08%), and runs rising more than 0.150 m (6 in) need handrails on both sides, 865–965 mm (34–38 in) high, plus edge protection. Slopes steeper than 1:8 are not allowed. Other countries have their own rules (e.g. Approved Document M in England, ISO 21542, national building codes): always check the code and edition that apply where you build.
More tools converter % ↔ degrees ↔ 1:x · grade-line elevations by station · ADA runs and landings
Quick converter
Type in any of them: the other two follow. 100% = 45°; 8.33% = 1:12.
A positive grade goes up, a negative one goes down. Stations are shown as chainage km+m (0+065.00 = 65 m from the start); use any interval.
Splits the rise into runs within the ADA limit and adds the landings.
Fill in the fields.
How to calculate a ramp
There are only three measurements: the rise (h), the horizontal length or run (L) and the slope (s, in %). Knowing two, you can work out the third:
- Slope: s = h ÷ L × 100. E.g. it rises 0.60 m over 7.20 m → 0.60 ÷ 7.20 × 100 = 8.33%.
- Length: L = h ÷ s × 100. E.g. rising 0.60 m at 8.33% → 0.60 ÷ 8.33 × 100 = 7.20 m.
- Rise: h = L × s ÷ 100. E.g. 5.00 m of ramp at 8.33% → 5.00 × 8.33 ÷ 100 = 0.42 m.
In degrees: angle = arctan(h ÷ L), so 8.33% ≈ 4.76°. Percent is not degrees: 100% is 45°, not 90°. A tape laid on the ramp surface measures √(L² + h²), always a little more than the horizontal length. In imperial units it works the same way: 1:12 means 1 in of rise for every 12 in (1 ft) of run.
FAQ
How do I calculate the slope of a ramp in percent?
Divide the rise by the horizontal length (run) and multiply by 100. E.g. it rises 0.60 m over 7.20 m → 0.60 ÷ 7.20 × 100 = 8.33%. If you measured along the sloped surface, the difference is small on gentle ramps, but the correct calculation uses the horizontal length.
How long must a ramp be to rise 1 metre?
At the steepest accessible slope (1:12 = 8.33%), 1.00 m ÷ 8.33 × 100 = 12.00 m of ramp. But under the ADA a single run may rise at most 0.760 m (30 in), so 1 m takes 2 runs of 6.00 m with a 1.525 m (60 in) landing between them: 13.53 m in total. In imperial units: every inch of rise needs a foot of run, so a 30 in rise needs a 30 ft run.
What is the maximum ramp slope under the ADA?
For a ramp on an accessible route, a running slope of 1:12 (8.33%), with at most 0.760 m (30 in) of rise per run and landings at least 1.525 m (60 in) long at the top and bottom of every run; cross slope no steeper than 1:48. Slopes of 1:20 (5%) or flatter are walking surfaces, not ramps. In existing buildings where space is limited, the ADA allows 1:10 for a rise of up to 150 mm (6 in) and 1:8 for up to 75 mm (3 in). Other countries have their own rules (e.g. Approved Document M in England, ISO 21542), so always check the code that applies to your project.
How many degrees is an 8.33% (1:12) ramp?
About 4.76° (arctan 0.0833). Other values: 5% ≈ 2.86°, 10% ≈ 5.71°, 20% ≈ 11.31°, 100% = 45°.
What about driveway and garage ramps?
Vehicle ramps are not covered by the accessibility rules; they follow the local building or zoning code, which varies from place to place. Gentler transition sections at the top and bottom keep cars from scraping. Check with your local building department.
How do I make a grade-line elevation table?
Open “More tools” and choose “Grade line”: enter the start elevation, the grade (negative if it goes down), the total distance and the station interval. The calculator returns the elevation at every station (chainage) and you can copy it into Excel or download a CSV.