A spirit level, bubble level or simply a level is an instrument designed to indicate whether a surface ishorizontal (level) or vertical (plumb). Different types of spirit levels may be used by carpenters, stonemasons,bricklayers, other building trades workers, surveyors, millwrights and other metalworkers, and in somephotographic or videographic work.

Early spirit levels had very slightly curved glass vials with constant inner diameter at each viewing point. They have a slight upward curve, so that the bubble naturally rests in the center, the highest point. At slight inclinations the bubble travels away from the marked center position. le.

An extension of the spirit level is the bull's eye level: a circular, flat-bottomed device with the liquid under a slightly convex glass face with a circle at the center. It serves to level a surface across a plane, while the tubular level only does so in the direction of the tube.