Question 1001787

A steeply sloped wheelchair ramp is very difficult to climb and can result in tipping or rolling backwards without control. 

You want to use the lowest slope possible which means building the longest ramp possible space permitting. 

For access to public places the maximum wheelchair ramp slope is 1:12. That means, for every 1 foot of ramp height from the ground, you ramp must be at least 12 feel long. 
If your porch decking material is 2 feet from the ground you would need, as a minimum, 24 feet of ramp based on a 1:12 slope requirement.
 Although 1:12 is the maximum slope, it is not ideal in most situations. A 1:18 or 1:20 is better. If you live in wet and icy climates, you will need more wheelchair ramp slope and rougher surfaces to prevent wheels from slipping.