Ramp Length & Gradient Calculator

Q: What is a 1:12 ramp?

One unit of rise per 12 units of run, which is 8.33% . It is the maximum slope for wheelchair ramps under the US ADA guidelines; many countries use similar or stricter limits.

Enter the vertical rise and the horizontal run to get the gradient in percent and degrees, plus the length of the ramp surface itself.

Reviewed by the WorldCalcs team · Methodology · Last reviewed: September 2026

Quick answer

Ramp gradient = rise ÷ run × 100. Example: 1 m of rise over 12 m of run is a 1:12 ramp = 8.33% ≈ 4.76°, with a ramp surface length of about 12.04 m.

Rise (vertical height)The height the ramp has to climb.Run (horizontal length)The horizontal distance available — same unit as the rise.

Gradient

8.33%

Angle: 4.76°
Ratio: 1:12
Ramp length: 12.04

Gradient % = rise ÷ run × 100 · Angle = atan(rise ÷ run) · Ramp length = √(rise² + run²)

This tool is for planning. Building codes, accessibility regulations and equipment limits govern what you are actually allowed to build and drive on — check the rules that apply where you are, and the manufacturer's limits for any machine using the ramp. See our Disclaimer.

Three ways to describe the same slope

A ramp gradient can be written as a percentage, as an angle in degrees, or as a ratio like 1:12. They all describe the same triangle: the rise is the vertical side, the run is the horizontal side, and the ramp surface is the sloping side that people and machines actually travel on.

Percent is rise ÷ run × 100. The angle is atan(rise ÷ run) converted to degrees. The ratio is simply 1 to the run divided by the rise. The ramp surface length is √(rise² + run²), which is always a little longer than the run — worth remembering when you are ordering material or checking that the ramp fits.

1:12 and accessibility limits

1:12 — one unit of rise per twelve units of run, or 8.33% — is the maximum slope for wheelchair ramps under the US ADA guidelines. Many countries use similar or stricter limits, so it is a useful benchmark even outside the United States.

For loading ramps the governing number is not an accessibility rule but the machine manufacturer's limit. Steeper ramps reduce stability and traction, and a loaded machine behaves differently from an empty one. Check the equipment documentation and the local building code before committing to a gradient.

Worked example

A doorway sits 1 m above the pavement and there is 12 m of ground available. The gradient is 1 ÷ 12 × 100 = 8.33%, the angle is atan(1 ÷ 12) ≈ 4.76°, and the ramp surface itself measures √(1² + 12²) = √145 ≈ 12.04 m — slightly longer than the run, because it is the sloping side of the triangle.

The same arithmetic works backwards when the gradient is fixed and you need to know how much room the ramp will take. Suppose the rise is 0.5 m and the ramp must not exceed 6%: the run required is 0.5 ÷ 0.06 = 8.33 m. Enter 0.5 and 8.33 above and the gradient comes back as 6%.

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Results are estimates and may contain errors — for general information only, not professional advice. Always verify before relying on them. Disclaimer

How to use

Measure the rise — the vertical height the ramp has to climb, from the lower surface to the upper one.

Measure or choose the run — the horizontal distance available on the ground for the ramp to cover that height.

Use the same unit for both. Metres, centimetres, feet or inches all work, as long as you do not mix them: the percentage and the angle come out the same either way, and the ramp length comes back in whatever unit you entered.

Read the gradient in percent, the angle in degrees, the 1:x ratio and the ramp surface length.

Frequently asked questions

What is a 1:12 ramp?+

One unit of rise per 12 units of run, which is 8.33%. It is the maximum slope for wheelchair ramps under the US ADA guidelines; many countries use similar or stricter limits.

What is the difference between percent and degrees?+

Percent is rise ÷ run × 100; degrees is the angle itself. They are not interchangeable — 100% equals 45°, not 90°. See the slope calculator if you are working with line gradients rather than ramps.

What gradient suits a loading ramp?+

It depends on the equipment — follow the machine manufacturer's limits. Steeper ramps reduce stability and traction, so the safe maximum for a loaded machine is often well below what the ramp itself could physically handle.

Why is the ramp length longer than the run?+

Because the ramp surface is the hypotenuse of the triangle formed by the rise and the run: √(rise² + run²). See the Pythagorean theorem calculator for the underlying maths.

Do rise and run have to be in the same unit?+

Yes — use the same unit for both. The percentage and the angle are unit-independent, and the ramp length comes back in whichever unit you entered.

References

US Department of Justice — 2010 ADA Standards for Accessible Design (ramp slope 1:12 maximum), ada.gov.
Basic trigonometry — gradient, angle and hypotenuse of a right triangle.