Common Unit Systems
A unit is a standardized quantity used to express a physical or abstract measurement. Throughout human history, different cultures and regions have developed their own unit systems. Today, the global standard is the International System of Units (SI), but many other systems remain in everyday use.
SI (Metric) System
The modern form of the metric system, adopted internationally. The seven base units are: meter (length), kilogram (mass), second (time), ampere (electric current), kelvin (temperature), mole (amount of substance), and candela (luminous intensity). All other units are derived from these.
Imperial System (UK)
Originated in medieval England and used today primarily in the United Kingdom. Includes units like the pound, foot, gallon (Imperial), and stone.
US Customary System
Derived from the English system but with some different standards. Includes the US gallon, US pint, US ton, and others. Despite sharing names with Imperial units, US customary units are often slightly different.
Natural & Scientific Units
Used in physics and chemistry: Planck units, Bohr radius, electron volt, atomic mass unit, light-year, parsec, astronomical unit.
Historical Units
Many ancient units are still encountered in literature, scripture, and classical studies: Roman actus, biblical shekel and talent, Greek cubit, Egyptian cubit, Russian archin, etc.
How to convert between systems
The general approach: identify the source unit, look up its conversion factor to a base unit (or to the destination unit directly), then multiply. UnitSwiftPro handles all of this for you automatically — just pick the units and enter a value.