The number of spans in a bridge is the number of distinct segments within the bridge structure which span any distance between ground supports. Distinct spans are demarcated either by points where the bridge makes contact with the ground itself, or points where the bridge deck is supported from below by piers, shear walls, embankments, and so on.

The count concerns segments between ground-support points. Contact with the ground itself can define an end, as can a pier, wall, or embankment supporting the bridge.

The number of movable leaves instead counts operating deck sections of a movable bridge. A span is defined by its supports, not by whether part of the deck moves.