Molecular Weight Calculator

Common Organic Compounds


Elements of the periodic table


Chemical formula:

Molecular weight, also known as molar mass, is the mass of a molecule or compound expressed in atomic mass units (amu) or grams per mole (g/mol). It is calculated by summing up the atomic masses of all the atoms in the molecule.

The atomic mass of an element is the average mass of its isotopes, taking into account their relative abundances. The atomic masses of elements can be found on the periodic table. To determine the molecular weight of a compound, you multiply the atomic mass of each element by the number of atoms of that element in the compound, and then sum up these values.

For example, let's calculate the molecular weight of water (H2O):

The atomic mass of hydrogen (H) is approximately 1.008 amu.
The atomic mass of oxygen (O) is approximately 15.999 amu.
To calculate the molecular weight of water:
(2 * 1.008 amu) + (1 * 15.999 amu) = 18.015 amu or g/mol

Therefore, the molecular weight of water is approximately 18.015 g/mol.

Molecular weight is an important property in various scientific fields, particularly in chemistry and biochemistry, as it is used to determine the amount of a substance needed for reactions and to convert between mass and moles in chemical calculations.


What is molecular weight?

Molecular weight is the sum of the atomic weights of all the atoms in a molecule.

How to calculate molecular weight?

Molecular weight can be calculated by adding the atomic weights of all the atoms in a molecule.