2010 ADA Standards for Accessible Design Pocket Guide
Detectable warnings shall consist of a surface of truncated domes and shall comply with 705.
Truncated domes in a detectable warning surface shall have a base diameter of 0.9 inch (23 mm) minimum and 1.4 inches (36 mm) maximum, a top diameter of 50 percent of the base diameter minimum to 65 percent of the base diameter maximum, and a height of 0.2 inch (5.1 mm).
Truncated domes in a detectable warning surface shall have a center-to-center spacing of 1.6 inches (41 mm) minimum and 2.4 inches (61 mm) maximum, and a base-to-base spacing of 0.65 inch (17 mm) minimum, measured between the most adjacent domes on a square grid. [S.H. 4.29.2]
Detectable warning surfaces shall contrast visually with adjacent walking surfaces either light-on-dark, or dark-on-light.