Molar mass is the mass (in atomic mass units) of one mole of a substance. One atomic mass unit (u) is equal to 1/12 the mass of one atom of carbon-12. Thus, the molecular weight of a molecule is the total number of protons and neutrons in all the atoms in that molecule.

Formula:

Molar Mass of a Gas (Dalton) = ( V * 0.0821 * ( G / T ) * P )

Where,
V -> Volume
G -> Mass of Gas
T -> Temperature
P -> Pressure