Measure on a map the distance between the two points you want to find the percent grade to find the run. For example, assume it is two miles.
Determine the change in elevation between the two points to find the rise. This is elevation at point 2 minus elevation at point 1. In the example, assume the change in elevation is 0.5 miles.
Divide the rise by the run. In the example, 0.5 miles divided by two miles equals 0.25 or a 25 percent grade.