2019 California Standards for Accessible Design Guide (effective January 1, 2020 with July 1, 2021 amendments)

11B-407.2.1.2 Size and shape.

Call buttons shall have square shoulders, be ¾ inch (19.1 mm) minimum in the smallest dimension and shall be raised ¹/₈ inch (3.2 mm) plus or minus ¹/₃₂ inch (0.8 mm) above the surrounding surface. The buttons shall be activated by a mechanical motion that is detectable.

[2010 ADA Standards] 407.2.1.2 Size. Call buttons shall be ¾ inch (19 mm) minimum in the smallest dimension.

Exception: Reserved.

[2010 ADA Standards] EXCEPTION: Existing elevator call buttons shall not be required to comply with 407.2.1.2.