Mole Calculator

Mole and molar mass: n = m / M

A mole is just a count: 6.022·10²³ entities, which is Avogadro's constant, N_A. Those entities can be atoms, molecules, ions, whatever you happen to be counting. Molar mass M is how many grams 1 mol of a substance weighs, and it comes out numerically equal to the atomic or molecular mass in u (unified atomic mass units). Take water, H₂O: its M is about 18 g/mol (2·1 + 16), so 18 g of water holds 1 mol, or 6.022·10²³ molecules. A mole of an ideal gas at STP (0 °C, 1 atm) takes up 22.4 L. Putting it together gives you n = m/M = N/N_A = V/V_m. Stoichiometry leans on moles to tie reactants to products through the coefficients of a balanced equation. That is what connects the mass you weigh out at the bench to the actual number of particles taking part in the reaction.

Applications

You will run into this in quantitative chemical analysis, in working out pharmacology doses, in industrial formulation, and in drug analysis under ANVISA. It also shows up when you prepare standard solutions for a titration, when chemical engineers figure gas volumes, and across the life sciences, from enzyme kinetics to the molarity of a buffer.

FAQ

How do I find the molar mass? Add up the atomic mass of each element in the formula, with each one multiplied by its subscript. So for H₂SO₄ you get 2·1 + 32 + 4·16 = 98 g/mol.

Mole or molecule? A mole is a way of counting, the same way "dozen" is. 1 mol of water means 6.022·10²³ water molecules.

Does 22.4 L work for any gas? Only at STP, and only if you treat the gas as ideal. Once you have a real gas at high pressure or low temperature, reach for an equation of state instead (PV = nRT or van der Waals).