measurement

Measurement is the process of assigning a numerical value to a property of an object or phenomenon by comparing it with a standard unit. A measurement comprises a quantity, a unit, and an estimate of the uncertainty in the result. Measurements enable quantitative comparison, replication, and communication across people and disciplines.

The International System of Units (SI) provides base units for seven quantities: meter, kilogram, second, ampere, kelvin, mole, and candela, together with many derived units. Units are defined and maintained by national metrology institutes and international organizations. All measurements should be traceable to these standards, forming a calibration chain that justifies reported values.

Outcomes of measurement include accuracy (closeness to the true value), precision (repeatability), and uncertainty (the range within which the true value is expected to lie). Measurement is influenced by instrument quality, method, environment, and observer. The typical process includes choosing a suitable instrument, taking readings, and estimating uncertainty.

Metrology is the science of measurement. It covers scientific metrology (the development of standards), industrial metrology (quality control in manufacturing), and legal metrology (measurement for trade and safety). Measurements underpin science, engineering, commerce, and everyday life, from length and mass to timekeeping and chemical concentration.