Molarity Calculator
mass = concentration × volume × molecular weight, solved live. Or switch to mass concentration to convert µg/mL and mg/mL.
Always use the batch-specific molecular weight from the vial label and CoA.
1 mg/mL equals 1 g/L. 1 µg/mL equals 1 mg/L. Molarity is that mass concentration divided by the molecular weight.
Runs entirely on your device - nothing is ever uploaded.
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How to use the molarity calculator
- Enter any three of mass, concentration, volume, and molecular weight.
- Pick the unit next to each value; mg with mM and mL convert automatically.
- Leave the value you want blank. It solves itself and is highlighted, scaled to a readable unit.
- Fill all four to check a preparation instead: you get Balanced or the percentage it is off.
- For µg/mL or mg/mL, switch to Mass concentration, enter the molecular weight, and leave either the mass concentration or the molarity blank.
Worked examples
Mass from scratch: a 197.13 g/mol compound at 10 mM in 10 mL needs 0.01 × 0.01 × 197.13 = 19.713 mg. Solvent from a weighed solid: dissolving 20 mg of it for a 10 mM stock takes 0.02 ÷ (0.01 × 197.13) ≈ 10.15 mL. Molarity from a preparation: 20 mg in 10 mL gives 0.02 ÷ (0.01 × 197.13) ≈ 10.15 mM.
µg/mL and mg/mL
Mass concentration and molarity are the same solution described two ways. In base units, g/L = mol/L × g/mol. 50 µg/mL of a 180.16 g/mol solute is 0.050 g/L ÷ 180.16 = 277.531 µM. The other direction: 10 mM of that solute is 0.010 × 180.16 = 1.8016 mg/mL. 1 mg/mL is exactly 1 g/L, and 1 µg/mL is exactly 1 mg/L, so those pairs are not a second conversion.
What it is for
Weighing out solids to make solutions of an exact molar concentration - stock solutions, buffers, dose-response series. Once the stock exists, the Dilution Calculator takes over for every working dilution via C₁V₁ = C₂V₂. For the mg/mL ↔ molarity bridge with dimensional analysis, see the guide How to convert mg/mL and µg/mL to molarity.