Wheelchair Ramp Length Calculator (1:12)

Understanding the wheelchair ramp length calculator — concept and principle

This calculator works out how long a ramp must be to climb a given height at a chosen slope, such as the 1:12 maximum used for wheelchair ramps. It also shows the sloped surface length, the grade in percent and degrees, and how many intermediate landings the US ADA rule and the Korean rule would require. Use it to plan a ramp at a shop entrance or a home step.

How it is calculated

Horizontal run L = rise × s, for a slope of 1:s

Surface length = √(L² + rise²)

Grade = 100 ÷ s (%) and angle = arctan(1 ÷ s)

Intermediate landings (ADA) = ⌈rise ÷ 76⌉ − 1 (not less than 0)

Intermediate landings (Korea) = the larger of ⌈rise ÷ 75⌉ − 1 and ⌈run ÷ 30 m⌉ − 1

• Rise is the vertical height to overcome, in cm.
• The slope 1:s means 1 unit up for every s units across.
• 76 cm is the ADA limit of 30 inches of rise for a single ramp run.

The principle

A slope ratio compares rise with run, so the run grows in direct proportion to the height. A 1:12 slope (8.33%, about 4.8°) is the steepest slope accessibility standards allow for new ramps, balancing ramp length against the effort of pushing a wheelchair up and braking on the way down. The sloped surface is the hypotenuse of a right triangle, so it is only slightly longer than the run for gentle slopes. Landings break long climbs into sections where users can rest, turn and stop safely.

Worked example

Default inputs: rise 30 cm, slope 1:12.

1. Run = 30 × 12 = 360 cm = 3.6 m.
2. Surface length = √(360² + 30²) = √130,500 ≈ 361.2 cm ≈ 3.61 m.
3. Grade = 100 ÷ 12 ≈ 8.3%; angle = arctan(1/12) ≈ 4.8°.
4. Landings: ADA ⌈30 ÷ 76⌉ − 1 = 0; Korea ⌈30 ÷ 75⌉ − 1 = 0 and ⌈3.6 ÷ 30⌉ − 1 = 0, so 0.

How to read the result

The run is the floor space the ramp needs, not counting the landings at the top and bottom, which are also required. Under the 2010 ADA Standards a ramp run may rise at most 30 inches (760 mm), landings must be at least 60 inches (1,525 mm) long, the clear width at least 36 inches (915 mm), and handrails are needed when the rise exceeds 6 inches (150 mm). Korean barrier-free rules also cap the slope at 1/12 and require a level landing for every 0.75 m of rise. Gentler slopes such as 1:16 or 1:20 are easier if space allows.

Common mistakes

• Forgetting top and bottom landings and the space to turn a wheelchair.
• Measuring rise from the wrong point instead of finished ground to finished threshold.
• Ignoring cross slope, drainage and slip resistance outdoors.

Frequently asked questions

How long should a ramp be for a 30 cm step?

At least 3.6 m of horizontal run at 1:12, plus landings.

What percent slope is 1:12?

8.33%, or about 4.76°.

How long is a ramp for 150 cm of rise?

18 m of run at 1:12, broken into sections with intermediate landings; often a lift is more practical for that height.

Sources: 2010 ADA Standards for Accessible Design, Section 405 (Ramps) · 장애인·노인·임산부 등의 편의증진 보장에 관한 법률 시행규칙 (Korean Enforcement Rule of the Act on Guarantee of Convenience Promotion for Persons with Disabilities, the Aged and Pregnant Women)