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How Does a Level Tool Work?

bubble level image by erbephoto from

A level tool provides builders with an essential piece of information: a surface's position relative to the earth's true horizon. In layman's terms, the level tells a builder if an object or surface sits at a flat, sloped or vertical position. The most common type of level is called a "spirit" level. Learning how a level tool works is relatively easy and, furthermore, it's an essential skill for many construction projects, including carpentry, plumbing and masonry.

Parts of a Level Tool

The basic level consists of two parts: a rectangular, bar-shaped body and a set of liquid-filled vials. The level's six-sided, bar-shaped body ranges in length from less than two feet to over four feet. A level typically contains two vials: a vial at the body's center and a vial at one end of the body. Longer levels often contain more vials. An air bubble exists within each liquid-filled vial.

How a Level Works

Like when air is released underwater, the bubble trapped within a level's vial strives to float upward. When the level's body and attached vial rest upon a sloping surface, the bubble floats toward the high side of the vial. If the level's body and attached vial rest upon a flat surface, the bubble remains at the vial's center. Gravity and the physical difference between gases and liquids control the function of the level. The level indicates "flatness" relative to the Earth's true horizon, rather than the Earth's uneven surface.

Applications of a Level

Levels appear in nearly every phase of construction. Prior to building, surveyors and engineers use levels to stake and survey building sites. Grading professionals often use levels to determine grading paths and concrete professionals rely on levels to create perfectly aligned foundations. Carpenters must master the operation of levels to build flat floors and plumb walls, while plumbers use levels to ensure that waste drains in the proper direction.

Types of Level Tools

Although level tools vary greatly according to application and appearance, most levels contain a spirit-filled vial. A surveyor's level often rests within a large, tripod-mounted assembly, called a "transit." To level strings and stakes across vast areas, grading professionals and concrete masons attach small spirit levels, called line levels, to string line. Carpenters, plumbers and other construction professionals typically use a rectangular spirit level, also called a builder's level.

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