Level

A level is a tool used to determine whether a surface is horizontal (level) or vertical (plumb). The most common type is the spirit level, which contains one or more vials of coloured liquid with an air bubble that moves to the centre when the surface is true.

How it works

A spirit level has a sealed glass or acrylic vial mounted in a straight body. The vial is filled with a low-viscosity liquid (usually coloured alcohol) with a small air bubble. When the level is placed on a horizontal surface, gravity pulls the liquid down and the bubble rises to the highest point — the centre of the vial if the surface is level. Graduated lines on the vial let you see exactly how far off level a surface is.

Types

• Spirit level (bubble level): The standard tool — a straight body with one or more vials. Common lengths are 2 feet, 4 feet, and 6 feet.
• Torpedo level: A small, compact level (about 9 inches) with three vials — horizontal, vertical, and 45°. Fits in a tool belt and is ideal for pipe and conduit work.
• Line level: A small spirit level that hangs from a string stretched between two points, used for establishing a level line over long distances.
• Laser level: Projects a visible laser line or dot, allowing one person to establish level over distances that would require a very long spirit level. Self-levelling models use a pendulum or electronic sensor to automatically compensate for tilt.
• Water level: A clear tube filled with water, used to transfer a level reference between two points that cannot be connected by a straightedge. Based on the principle that water finds its own level.

Plumb vs. level

“Level” means horizontal — perpendicular to the direction of gravity. “Plumb” means vertical — parallel to gravity. A level typically has at least two vials: one for checking level and one for checking plumb.