Beam balance (or beam scale) is a device for measuring weight or mass. They are also called mass scales, weight scales, mass balances, weight balances, or simply scales, balances, or balance scales.

A traditional scale consists of two plates or bowls suspended at equal distances from a control point. One plate contains an object of unknown mass (or weight), while known masses are added to the other plate until static equilibrium is reached and the plates level off, which occurs when the masses on both plates are equal. The perfect scale rests at neutral. A spring rock will use a spring of some hardness to determine mass (or weight).

Suspending of a given mass will lengthen the spring by a certain amount depending on the hardness of the spring (or constant spring). The heavier the object, the more the spring stretches, as described in Hooke’s law. There are other types of scales using different physical principles.

Some scales may be calibrated to read in units of force (weight), such as newtons, instead of mass units, such as kilograms. Scales and scales are widely used in trade, as many products are sold and packaged by mass.

The initial shape of the balance consisted of a beam with a fulcrum in the center. For maximum accuracy, the support will consist of a sharp V-joint placed in a smaller V-bearing. To determine the mass of an object, a combination of control masses was hung on at one end of the beam, and an object of unknown mass was hung on at the other end. For high-precision work such as empirical chemistry, the balancing beam is still one of the most accurate technologies available and is commonly used to calibrate test masses.

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