Case 1
- Rise to climb
- 30cm
- Slope ratio (run per unit of rise)
- 12
361.25cm
Open with these valuesRamp Length Calculator
361.25cm
Result: 361.25 cmThe ramp you build is the hypotenuse, not the floor distance. A 30 cm rise at the ADA maximum of 1:12 covers 360 cm of floor and measures 361 cm along the slope. Enter the rise in centimetres; the ratio is how many units of run you allow for each unit of rise.
The numbers at a glance
Held fixed: Rise to climb 30.0 cm.
| Slope ratio (run per unit of rise) | Result (cm) |
|---|---|
| 6.0 | 182.48 |
| 8.0 | 241.87 |
| 10.0 | 301.50 |
| 12.0Your value | 361.25 |
| 14.0 | 421.07 |
| 16.0 | 480.94 |
| 18.0 | 540.83 |
Worked examples
Case 2
- Rise to climb
- 15cm
- Slope ratio (run per unit of rise)
- 12
180.62cm
Open with these valuesCase 3
- Rise to climb
- 10cm
- Slope ratio (run per unit of rise)
- 8
80.62cm
Open with these valuesHow it's calculated
length = √(rise² + (rise × ratio)²)
- StepMeasure the vertical rise in centimetres — a step, a threshold, a porch.
- StepSet the slope ratio: 12 for the ADA 1:12 maximum, 16 or 20 for an easier ramp.
- StepThe run is rise × ratio; the ramp is the hypotenuse of rise and run.
- ResultAbove 76 cm of rise a level landing is required, so split the climb into runs.
What this number means
The applicable standard decides, not this page
The calculator returns geometry and enforces no slope of its own. The 1:12 default is the ADA maximum and applies in the United States, while accessibility in Germany is governed by DIN 18040, which allows a 6 % longitudinal slope. Settle which rule binds your build before you fix a ratio.
You build the hypotenuse, not the floor run
A 30 cm rise at 1:12 covers 360 cm of floor, and the ramp surface measures 361.25 cm. The run is what you need for the footprint, the ramp length is what you cut and lay.
Enter the run side of the ratio
For 1:12 the field takes 12, not 8.33 and not 4.8. It is how many units of run you allow for each unit of rise, and it carries no unit of its own.
One straight run, no landings
The source puts the maximum rise of a single run at 30 inches, about 76 cm, before a level landing is required, and landings also belong at the top, the bottom and every change of direction. This calculator gives the geometry of one straight run and enforces none of that.
Commonly misread
1:12 is 8.33 %, so I entered 8.33.
The field takes the run side of the ratio, which is 12 for 1:12. Entering 8.33 gives a run of about 250 cm for the same 30 cm rise, a much steeper ramp.
The run is 360 cm, so a 360 cm ramp section is what I need.
You build the hypotenuse, which comes to 361.25 cm here. The run is the floor distance the ramp spans, not the length of the surface itself.
1:12 is the safe slope wherever I build.
It is the ADA maximum and applies in the United States, while DIN 18040 governs in Germany and allows a 6 % longitudinal slope. Which standard binds you depends on where and what you build.
A rise of 120 cm gets one long ramp in a single run.
The source caps a single run at 30 inches of rise, roughly 76 cm, before a level landing is required. Split the climb into runs with landings between them.
Reference table
| Rise, ratio | Horizontal run | Ramp length (cm) |
|---|---|---|
| 10, 8 | 80 cm | 80.62 |
| 15, 12 | 180 cm | 180.62 |
| 30, 12 | 360 cm | 361.25 |
| 30, 16 | 480 cm | 480.94 |
| 100, 12 | 1200 cm | 1204.16 |
Questions
How do I calculate ramp length?
Multiply the rise by the slope ratio to get the horizontal run, then take the hypotenuse: length = √(rise² + run²). A 30 cm rise at 1:12 needs a 360 cm run and about 361 cm of ramp.
What slope does the ADA allow?
A running slope of 1:12 at most, which is 8.33 % or about 4.8 degrees, so enter 12 for that limit. The Access Board recommends going gentler wherever space allows and suggests 7.5 % for exterior ramps.
What is the difference between the run and the ramp length?
The run is the floor distance the ramp covers; the ramp length is the sloped surface you actually build and travel on. The ramp is always slightly longer, because it is the hypotenuse of rise and run.
Do I need landings on a long ramp?
Yes. A single run may climb at most 30 inches, about 76 cm, before a level landing is required, and landings are needed at the top, the bottom and every change of direction. This calculator gives the geometry of one straight run only.
Which unit should I use for the rise?
Centimetres, and the run and ramp length come back in centimetres too. The slope ratio has no unit, so only the proportion of run to rise matters — the same 12 works whatever you measure the height in.
Sources and last check
Information, not professional advice.