What is a measurement unit?
A measurement unit is a defined quantity used as a reference for expressing and comparing physical measurements. A numerical value without a unit does not fully describe a physical measurement.
Standardized units allow measurements performed in different places and at different times to be compared consistently. The International System of Units provides the primary measurement framework used in science and engineering.
Metric and imperial units
Metric units use decimal relationships based on powers of ten. Prefixes such as kilo, centi and milli indicate multiples or subdivisions of a base unit.
Imperial and United States customary units include measurements such as the foot, mile and pound. Defined conversion factors are required when converting between these systems and metric units.
Unit symbols
Unit symbols are standardized abbreviations. Symbols are case-sensitive and normally remain unchanged in the plural. For example, meter is represented by m, kilometer by km and kilogram by kg.