What is the 1:12 ramp rule?
The core ADA ramp rule limits the running slope of an accessible ramp to a maximum of 1:12. In practical terms, that means for every 1 inch of rise, you need at least 12 inches of horizontal run. A 24 in rise requires a minimum of 24 ft of ramp run. This corresponds to a slope of 8.33%, which is steep enough to move people efficiently but still manageable for most wheelchair users and people with limited mobility.
The ADA also limits cross slope to 1:48 (about 2%) so that users do not feel like they are being pulled sideways off the ramp surface.
Key requirements at a glance
- Maximum running slope: 1:12 (8.33%). Gentler slopes such as 1:16–1:20 are preferred where space allows.
- Maximum rise for any single ramp run: 30 in. Higher total rises must be broken into multiple runs with landings.
- Minimum clear width between handrails: 36 in.
- Maximum cross slope: 1:48 (≈ 2%) to prevent side drift.
When are handrails and landings required?
ADA and IBC do not require handrails and landings on every single sloped surface. They are triggered once a ramp is long or steep enough that it becomes difficult or unsafe to navigate without support.
Handrails are typically required when:
- The ramp rise is greater than 6 in, or
- The horizontal projection is greater than 72 in.
- In those cases, provide handrails on both sides, at 34–38 in height, with 12 in minimum extensions and returned ends to prevent clothing from catching.
Landings are required:
- At the top and bottom of each ramp run.
- Where the ramp changes direction (for example, 90 deg or switchback turns).
- Where the total rise exceeds 30 in, an intermediate landing is required so that no individual run rises more than 30 in.
- Landings must be at least 60 in long in the direction of travel and at least as wide as the ramp they serve.
How this relates to the calculator
The ADA Ramp Calculator uses these same 1:12 slope limits and handrail/landing triggers to evaluate your design. When you enter a total rise, available run and configuration, the tool:
- Checks whether a 1:12 ramp can physically fit within the available run.
- Breaks the total rise into runs so that no single run rises more than 30 in.
- Determines whether handrails are required based on ramp rise and length.
- Calculates where landings are needed and how many landings are required.
If your input does not meet these rules, the calculator will surface warnings and checklist items so you can quickly adjust the geometry before you commit it to drawings.
This guide is a simplified summary of selected ADA 2010 and IBC 2021 ramp provisions. Always verify requirements with the adopted codes in your jurisdiction and the local building official.