Units & The Metric System A unit simply describes what a number represents: amount, speed, dollars etc. Scientists use a standard set of units to describe their observations and make calculations. Agreeing upon standard units has many advantages, especially when communicating your results to others. The standard units scientists use in their measurements and calculations are called The International System of Units or S/ units for short. The other system of units you are familiar with are part of the British System. Physical Property Distance SI unit meters British Unit Feet (or inches) Equality 1 meter = 3.78 ft Volume Mass Time liter Kilogram Second Kelvin Joule Temperature Energy