Definition
Depth
Depth is a length measured inward, downward, or from front to back from a chosen surface.
What it means
Depth answers “How far in?” or “How far down?” A pool’s depth is measured from the water surface to the bottom; a box’s depth may be measured from front to back.
Remember it
Start at a surface, then measure in or down.
Example
The water surface is at the 0 cm mark and the bottom is at 75 cm, so the water depth is 75 cm.
Watch for
Depth is a length, not the amount of space inside an object; that amount is volume.
Common mix-up
Width, height, and depth name different directions, so the object or diagram must show which direction is meant.
Exact meaning
Depth is a length dimension measured from a stated surface or reference plane inward, downward, or from front to back. Its direction depends on the object and context.