The textbook discusses the basic concepts of measuring physical quantities and units of measurement, the principles of building a rational system of units. The International System of Units . has been systematically described. The main and derivative units of the system are described in detail, the formation of multiple and fractional units, their abbreviated designations. are considered. State standards and standards for units of measurement for certain types of measurements are analyzed. The order of use of units of other systems, as well as non-system units in addition to the International System. is considered.