This script is made up of two calculators. The first is designed to give the percent of grade change on highways located in mountain terrains. The calculation is good for inclines (uphill), sometimes called upgrades or declines (downhill), often called downgrades. It is based on how much vertical change in meters takes place, up or down, over a given horizontal distance. The horizontal distance is often difficult to determine as it is NOT based on driving distance (including curves in the road). It is based on straight line distance. The lower calculator is designed to give the actual distance change if you know the percentage and horizontal distance. Our example (in both calculators) is for a 1% downgrade (or incline). Over a 1 kilometer horizontal distance, if the elevation change is 10 meters, that is a 1% grade change. You may wish to use our standard (non-metric) version instead.
Special thanks to John Bevan, Ph.D., for his help on this calculator.
last updated 5/20/11