The range of allowed slope for a wheelchair ramp will depend on your local regulation. One of the most famous ones is the ADA Ramp Requirement code. It establishes the following limits:
Minimum slope: 1:20, meaning you will have 20 units of horizontal length (run) by 1 unit of vertical length (rise).
Maximum slope: 1:12, meaning you will have 12 units of horizontal length (run) by 1 unit of vertical length (rise).
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