Molarity Calculator
Concentration in mol/L from mass and volume, or the mass to weigh out for a target molarity.
The formula
M = (mass / molar mass) / volume
Dissolving 58.44 g of NaCl (its molar mass) in water up to 1 L gives exactly 1 mol/L, written 1 M. Working backwards: a 0.5 M solution in 250 mL needs 0.125 mol, which for NaCl is 7.3 g.
Lab notes
Volume means the final solution volume, not the water added: dissolve the solid in less solvent, then fill to the mark in a volumetric flask. Molarity also drifts slightly with temperature since solutions expand; for work where that matters, chemists switch to molality (mol per kg of solvent), which doesn't. For hydrated salts, use the molar mass including the water of crystallization printed on the bottle.