True vertical depth
![(a) is an imaginary line representing the true vertical depth, while line (b) is the borehole itself, and its length is called the measured depth.](/Images/godic/202502/18/True_vertical_depth2347.jpg")
True vertical depth is the measurement of a straight line perpendicularly downwards from a horizontal plane.
In the petroleum industry, true vertical depth, abbreviated as TVD, is the measurement from the surface to the bottom of the borehole (or anywhere along its length) in a straight perpendicular line represented by line (a) in the image.