<P> The metric system is an internationally adopted decimal system of measurement . It is in widespread use, and where it is used, it is the only or most common system of weights and measures . It is now known as the International system of units (SI). It is used to measure everyday things such as a sack of flour, the height of a person, a tank of petrol, and the speed of a car . It is also used in science, industry and trade . </P> <P> In its modern form, it consists of a set of electromechanical base units including metre for length, kilogram for mass, second for time and ampere as an electrical unit, and a few others, which together with their derived units, can measure any useful quantity . Metric system may also refer to other systems of related base and derived units defined before the middle of the 20th century, some of which are still in limited use today . </P> <P> The metric system was designed to have a set of properties that make it easy to use and widely applicable, including units based on the natural world, decimal ratios, prefixes for multiples and sub-multiples, and a structure of base and derived units . It also has a property called coherence, which means its units are related 1: 1, so that conversion factors are unnecessary . In science, it has a property called "rationalisation", which eliminates certain constants of proportionality in equations of physics . </P>

Standard unit of length in the metric system