depth

Depths are measurements below the base level of a structure taken along a radius from the center of the earth. Each depth measurement must have defined endpoints at the bottom and the top; usually the top point is the structure's base level.

Depths are measured in the same units as length, height, thickness, and elevation.

The deepest foundation member and the lowest usable floor can supply different lower endpoints. An elevation below sea level is a position relative to sea level and need not equal a depth below the structure's base.