⚗️ Molarity Calculator
Work out the molarity of a solution from mass, molar mass and volume — or find the mass to weigh out for a target molarity.
Molarity
molarity = (mass ÷ molar mass) ÷ volume
0.1 mol/L
Moles of solute
moles = mass ÷ molar mass
0.1 mol
To make it
mass = molarity × volume × molar mass
weigh 5.844 g into 1 L
How the molarity calculator works
Moles = mass / molar mass, and molarity = moles / volume (in litres). Enter mass, molar mass and volume to get the molarity; leave mass blank (0) and enter a target molarity to find the mass you need to weigh out. Because you supply the molar mass, it works for any compound.
A bench-chemistry staple used constantly in biology for buffer and reagent prep. You supply the molar mass, so there is no compound database to maintain.
Frequently asked questions
How do you calculate molarity?
Molarity (mol/L) = moles of solute / litres of solution, and moles = mass / molar mass. So molarity = mass / (molar mass × volume in litres).
How much do I weigh out for a given molarity?
Mass = molarity × volume (L) × molar mass. For 1 L of 0.1 M NaCl (molar mass 58.44 g/mol): 0.1 × 1 × 58.44 = 5.844 g.
What is the difference between molarity and molality?
Molarity is moles per litre of solution; molality is moles per kilogram of solvent. This tool computes molarity, which is what most lab recipes specify.
Where do I get the molar mass?
From the compound’s formula (sum of atomic masses) or the reagent bottle. NaCl is 58.44 g/mol, Tris is 121.14 g/mol, for example. You enter it, so any compound works.
What volume unit should I use?
Enter volume in litres. For millilitres, divide by 1000 first (e.g. 250 mL = 0.25 L).
Is molarity chemistry or biology?
Both — it is core chemistry, but it is used constantly in biology labs for preparing buffers, media and reagents, which is why it sits in the lab cluster here.