2010 ADA Standards for Accessible Design Pocket Guide
504.2 Treads and Risers.
All steps on a flight of stairs shall have uniform riser heights and uniform tread depths. Risers shall be 4 inches (100 mm) high minimum and 7 inches (180 mm) high maximum. Treads shall be 11 inches (280 mm) deep minimum. [S.H. 4.9.2]