Building Outdoor Stairs or Ramp - HomeTips15 Mar 2015 ... This will give you the total run. For example, let's say the total rise is 40 inches. 40 divided by 7 is 5.7. Rounding to 6 gives you the number of steps you will need. 10 times the number of treads, 5 (the number of steps minus 1), results in a total run of 50 inches. outdoor wood ramp construction diagram. To figure out the unit rise, or the rise of each step, simply divide the total rise40 inchesby the number of steps6. The unit rise is approximately 6 5/8 inches.