Molarity Calculator
Find the molarity of a solution from the mass of solute, its molar mass and the solution volume — with moles, g/L and millimolar alongside.
Moles of solute per litre, from what you weighed out.
How the molarity calculator works
Molarity is moles of solute per litre of solution. Divide the mass by the molar mass to get moles, then divide by the volume in litres. 5.85 g of NaCl (58.44 g/mol) in 250 mL is 0.1001 mol ÷ 0.25 L = 0.400 M.
Use the molar-mass calculator for the formula mass, and the solution-preparation calculator for the reverse question — how much to weigh out for a target molarity.
Formula: M = (mass ÷ molar mass) ÷ volume in litres
Worked examples
| Inputs | Molarity | Note |
|---|---|---|
| 5.85 g NaCl in 250 mL | 0.4004 mol/L | 0.400 M |
| 10 g glucose in 500 mL | 0.111 mol/L | 0.111 M |
| 4.0 g NaOH in 1 L | 0.1 mol/L | 0.100 M |
FAQFrequently asked questions
Is the volume the solvent or the solution?
The final solution. Dissolve the solute, then make up to the mark — the solute itself takes up some volume.
What is the difference between molarity and molality?
Molarity is moles per litre of solution; molality is moles per kilogram of solvent. Molality does not change with temperature, so it is used for colligative properties.
How do I convert mg/L to molarity?
Divide mg/L by 1,000 to get g/L, then by the molar mass. 100 mg/L of NaCl is 0.1 ÷ 58.44 = 0.00171 M.
What does M mean?
Moles per litre — "a 0.4 M solution" is 0.4 mol/L.
Where these figures come from
- IUPAC — Standard atomic weights (2021 conventional values) — the molar-mass table
- NIST — CODATA 2018 fundamental physical constants — Avogadro constant, gas constant, speed of light
- NIST Chemistry WebBook — thermochemical data
- CSIRO — Australia's national science agency
Last checked: September 2026. Atomic masses are the IUPAC conventional values; constants are CODATA 2018; equations are the standard textbook forms.