Definition of Rise and Run
Any ramp or other sloped surface can be described in terms of rise and run. The rise is the vertical distance between a ramp's top and bottom, while the run is the horizontal distance from the ramp's start to end, measured perpendicular to the run.
Calculating Rise and Run
A ramp's slope is calculated by dividing the rise by the run---a formula commonly used to calculate the run required for needed rise. ADAAG sets the maximum slope for a handicapped ramp at 1:12, meaning that for 1 inch of rise, a minimum 12-inch run is required.
Additional Installation Planning Factors
When calculating the entire space that a handicapped ramp installation requires, it is important to note that ADAAG limits single continuous ramps to 30 inches maximum in height. Greater rise requires multiple ramps built with 60-inch minimum length landings between.
ADAAG's guidelines hold additional clearance requirements for various ramp configurations.