2010 ADA Standards for Accessible Design Pocket Guide
306.2 Toe Clearance.
Space under an element between the finish floor or ground and 9 inches (230 mm) above the finish floor or ground shall be considered toe clearance and shall comply with 306.2.
Toe clearance shall extend 25 inches (635 mm) maximum under an element.
Where toe clearance is required at an element as part of a clear floor space, the toe clearance shall extend 17 inches (430 mm) minimum under the element.
Space extending greater than 6 inches (150 mm) beyond the available knee clearance at 9 inches (230 mm) above the finish floor or ground shall not be considered toe clearance.
Toe clearance shall be 30 inches (760 mm) wide minimum.