Last updated: 2026-07-13

Solution Concentration

Solution concentration can be reported three ways, and moving between them is a routine step when preparing reagents, reading a label, or checking a protocol. This converter takes one known value — mass concentration in grams per litre, molarity in moles per litre, or mass percent — and returns the other two. The default mode assumes the known value is g/L; the mass-percent and molarity modes swap which field is the input.

Definitions

The three quantities describe the same solution from different angles.

• Mass concentration ($\gamma$, g/L) is the mass of dissolved solute per litre of solution.
• Molar concentration ($c$, mol/L, also written M) is the amount of solute in moles per litre of solution.
• Mass percent ($w$) is the solute mass as a fraction of the total solution mass, expressed as a percentage.

Two properties of the solute and solution link them: the molar mass $M$ (g/mol) connects mass to moles, and the solution density $\rho$ (g/mL) connects a volume of solution to its mass.

Formula

The mass–mole conversion needs only the molar mass:

Mass percent compares solute mass to solution mass. One litre of solution has a mass of $1000\,\rho$ grams when $\rho$ is in g/mL, so the mass fraction is:

Combining the two gives the direct molarity ⇄ mass-percent path, which always routes through g/L.

Worked example

Sodium chloride has a molar mass of 58.44 g/mol. A solution of 58.44 g/L at a density of 1.037 g/mL converts as follows.

So 58.44 g/L of sodium chloride is a 1 mol/L (1 M) solution, and roughly 5.64 % by mass.

When each unit is used

Mass concentration in g/L is convenient for weighing out a solid, since it states grams directly. Molarity is the working unit for reaction stoichiometry, because reactions combine species in mole ratios. Mass percent appears on commercial reagent labels and in food or cleaning products, where the total mass of the mixture is the natural reference. Because the three describe one physical solution, a protocol written in one unit can always be reproduced in another once the molar mass and density are known.

Notes on accuracy

The molarity conversion is exact given the molar mass. The mass-percent conversion depends on the solution density, which changes with concentration and temperature — a concentrated solution is denser than a dilute one. For dilute aqueous solutions the density is close to 1.0 g/mL, and using that value keeps the mass percent within a fraction of a percentage point. For concentrated solutions, use the density measured at the working temperature for the best result. This tool does not model temperature effects; enter the density that applies to the solution being prepared.

Related calculators

Molarity Calculator works from moles and volume directly, and Serial Dilution Calculator handles step-by-step dilution series. For pure mass-per-volume density conversions, see Density Converter.