Tread Depth (Going)
Horizontal depth of a step, measured on the walking line.
The tread depth — also called the going — is an important dimension of a staircase. It denotes the horizontal depth of a step measured along the walking line from the nosing of one step to the projected nosing of the next. Nosing projections are not included. DIN 18065 specifies minimum and maximum values for required residential staircases; for example, the going must be between 230 mm and 370 mm.