Molarity calculator for mass, volume, concentration, and molecular weight

How the molarity calculator solves mass, concentration, and volume

Molarity describes the amount of substance in moles divided by the total volume of solution in liters. When a compound is measured by mass, molecular weight connects grams to moles. Multiplying molar concentration by solution volume gives the number of moles required, and multiplying those moles by molecular weight gives the required mass in grams.

The same relationship can be rearranged for three common laboratory questions. To find mass, multiply concentration, volume, and molecular weight. To find concentration, divide mass by volume and molecular weight. To find volume, divide mass by concentration and molecular weight. The selector above makes the chosen unknown explicit instead of relying on an empty-field convention.

All values are converted to base units before the equation runs: concentration to mol/L, volume to liters, and mass to grams. The answer is then converted back to the unit selected beside the output field. This allows inputs such as mg, mM, and mL to be used without manual prefix conversion.

Molarity calculator example for compound mass in milligrams

For a compound with a molecular weight of 197.13 g/mol, preparing 10 mL of a 10 mM solution requires 19.713 mg. The normalized calculation is 0.010 mol/L × 0.010 L × 197.13 g/mol = 0.019713 g. Converting grams to milligrams produces 19.713 mg.

The displayed precision should not be mistaken for achievable weighing precision. Record a result using significant figures supported by the balance, volumetric equipment, product purity, and written procedure. A protocol may also require a correction for assay value or purity that is outside this calculator.

Reverse molarity calculations for concentration or solution volume

If compound mass, molecular weight, and solution volume are known, select Concentration. The calculator converts the mass to grams and divides it by volume in liters and molecular weight in g/mol. If mass, molecular weight, and desired concentration are known, select Volume to calculate the final solution volume.

The calculated volume is a final volume, not automatically an amount of solvent to pour into a container. Dissolving a solid can change solution volume, so laboratory procedures commonly dissolve the material and then bring the solution to a defined final volume. Follow the applicable product documentation and protocol for the preparation sequence.

Common molarity calculator mistakes with molecular weight and final volume

Keep molarity separate from mass concentration. A value in mg/mL cannot be entered as mM unless molecular weight is used to convert between mass and amount of substance. Likewise, molecular weight in g/mol is numerically compatible with daltons for many routine calculations, but the exact product form still matters.

Before using an answer, confirm the chemical formula, molecular weight, purity basis, concentration definition, final-volume convention, and whether the compound is soluble and stable in the selected solvent. This website verifies arithmetic relationships only and does not validate a formulation or experimental procedure.

• Use final solution volume, not the initial amount of solvent added to dissolve a solid.
• Use the molecular weight for the exact salt, hydrate, or conjugate being weighed.
• Do not enter mg/mL in a molarity field; convert it through molecular weight first.
• Round the result to the precision supported by the balance and volumetric equipment.