Mass Concentration to Molar Concentration Calculator
Convert mass concentration to molar concentration and back, using the molar mass — with the mass needed to make a given volume.
Molarity is mass concentration divided by molar mass: a solution at 40 g/L of a substance with molar mass 40 g/mol is exactly 1 M.
How the mass concentration to molar concentration calculator works
Molarity is mass concentration divided by molar mass: a solution at 40 g/L of a substance with molar mass 40 g/mol is exactly 1 M.
The practical direction is usually the reverse — how much to weigh out. To make 250 mL of 0.1 M from something with molar mass 180, you need 0.1 × 0.25 × 180 = 4.5 g.
Formula: M = (g/L) / molar mass; mass = M × V × molar mass
Worked examples
| Inputs | Result | Note |
|---|---|---|
| 40 g/L at molar mass 40 | 1 | exactly 1 M |
| 0.1 M glucose in 250 mL | 18.016 | weigh 4.5 g |
| Back the other way | 0.1 | 0.1 M |
FAQFrequently asked questions
How do I convert g/L to molarity?
Divide by the molar mass in g/mol.
How much do I weigh out?
Molarity × volume in litres × molar mass. 0.1 M in 250 mL of something at 180 g/mol needs 4.5 g.
What if my compound is hydrated?
Use the molar mass including the water of crystallisation. CuSO₄·5H₂O is 249.7 g/mol, not 159.6 — a 56% error if you get it wrong.
Should I make up to volume or add volume?
Make up to the mark. Dissolving solute changes the volume, so adding a litre of water to the solid does not give a litre of solution.
What about purity?
Divide by the stated purity. A reagent at 95% needs 5% more mass weighed out.
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.