Calibration weights (also known as reference weights or test weights) are known, standard weights, manufactured to very high tolerances and accuracy, used for the performance checking and calibration of analytical balances, precision balances and general-purpose scales in the research laboratory, educational settings and other working environments. They may also be used for the calibration of other improvised or unknown weights.

How are calibration weights made?

Calibration weights take the form of simple discs, cylinders, wires or leaves. Calibration weights are typically available as sets, often supplied with tweezers and gloves in a protective case for safe keeping. They may also be sold as individual weights. Calibration weights are often supplied as accessories for compatibility with specific makes and models of balance.

Calibration weights are made of metals such as polished brass, aluminium or special stainless steels for durability, anti-magnetisation, and resistance to corrosion or wear and tear that could affect accuracy. Calibration weights are available in nominal values of a few millligrams up to 10kg or more. They may also be supplied with appropriate certifications or statements of accuracy, compliance and traceability.

How are calibration weights classified?

Calibration weights are classified by organisations such as ASTM, OIML and NIST according to their accuracy. The appropriate classification depends on the resolution of the balance and the degree of accuracy needed to satisfy the particular weighing application. The principal classes are:

• Class M1 calibration weights are used with standard scales
• Class F1 calibration weights are used with precision electronic balances
• Class E2 calibration weights are used with highly accurate analytical balances