 # Know how to figure the percent slope of your trails?

Percent slope is determined with just two numbers. It is calculated using the amount of vertical distance (rise) over a given horizontal distance (run). Often called “rise over run,” the “rise” is divided by the “run.” For example, if the vertical rise is 10 feet over a distance of 100 feet, the math reads like this: 10 feet rise is divided by 100 feet run, then multiplied by 100 to create a percentage, which equals a 10% slope.

Two-part quiz:

• What is the percent of the slope for an area that has 3 feet of rise over 100 feet of run?
• And, if a trail is built, what is the percentage of cross slope necessary to adequately shed water trailside?

To calculate the slope for 3 feet of rise over 100 feet of run is: 3 divided by 100 equals 0.03, and multiplied by 100 to get the percentage, which is 3%.

To calculate cross slope is easy. The Rule of 1/3 states that the grade slope should be 1/3 of the cross slope. Or, stated another way, cross slope should be three times larger than grade slope. If the grade slope is 3%, then cross slope must be 3 times larger or 9%.