2010 ADAS 306.3.3 Knee Clearance Minimum Required Depth
Where knee clearance is required under an element as part of a clear floor space, the knee clearance shall be 11 inches deep minimum at 9 inches above the finish floor or ground, and 8 inches deep minimum at 27 inches above the finish floor or ground.
Code according to 2010 ADAS. Check your state’s accessibility laws. Some states such as California, Georgia and Florida have additional requirements and standards.