Mass is one of the basic measurements of the International System of Units, and it is calculated in kilograms (kg). Gram (g) equals to 1⁄1000 of a kilogram (or 1E - 3 kg). Other units used in SI: ton (t), electronvolt (eV) and atomic mass unit (a. m. u.). Also it is used a number of different mass designations, which are not included in the System of Units, for example, slug (sl) pound (lb), Planck mass (Mp) and solar mass. In normal conditions an object weight is proportional to its mass, making it easy to use the same units in both concepts.