For a permanent wheelchair ramp for public access it is usually best to use the lowest slope possible, which means, build the longest wheelchair ramp that you have space for. Why? A steep wheelchair ramp is difficult to climb and can be very dangerous because of the risk of tipping backwards.
The absolute maximum acceptable incline for a wheelchair ramp intended for public access is 1:12. This means that for every 1 foot in height the ramp must be at least 12 feet long or more (or for 2 feet in height the ramp must be at least 24 feet long, or for 1 meter in height it must be at least 12 meters long. See drawing to the right) and 1:18 is often recommended for the elderly. Even that will be too steep for some. In very wet or icy climates, less steep wheelchair ramps and rougher surfaces may be required to prevent wheel slippage. The ramps A, B and D in the photo below are much too steep to be of use as wheelchair ramps.