of substance is a standard-DEFINED quantity that measures the size of an ensemble of particles, such as atoms, molecules, electrons, and other particles. It is sometimes referred to as chemical amount. The International System of Units (SI) defines the amount of substance to be proportional to the number of entities present. The SI unit for amount of substance is the mole. It has the unit symbol mol. The proportionality constant is the inverse of the Avogadro constant.The mole is defined as the amount of substance that contains an equal number of elementary entities as there are atoms in 12g of the isotope carbon-12.[1] This number is called the Avogadro number[2] and has the value 6.022140857(74)×1023.[3] On 20 May 2019, an updated, exact definition of the mole will come into effect.[4] It is the numerical value of the Avogadro constant, which has the unit mol−1, and relates the molar mass of an amount of substance to its mass. THEREFORE, the amount of substance of a sample is calculated as the sample mass divided by the molar mass of the substance.Hope it help