milimolar

Millimolar (mM) is a unit of chemical concentration expressing the amount of solute per liter of solution. It denotes one thousandth of a mole per liter, i.e., 1 mM = 1×10^-3 mol/L. The symbol combines a lowercase m for milli and an uppercase M for molarity.

Millimolar is widely used in chemistry, biochemistry, medicine, and physiology to express concentrations of reagents, buffers, substrates, drugs, and ions in solutions. In biological contexts, many measurements are reported in mM because concentrations commonly fall in the millimolar range. For example, ions like sodium, potassium, and calcium are often described in millimolar terms in physiological studies.

To relate millimolar to other units, note that 1 mM equals 0.001 M. The mass concentration depends on the solute’s molar mass: a solution with X mM of a substance of molar mass M g/mol has X×M/1000 g per liter.

Preparing solutions often involves dilution. To make a desired mM solution from a stock solution, use the dilution relation C1V1 = C2V2, where concentrations are in the same units. For example, to obtain 10 mM from a 100 mM stock, mix 1 part stock with 9 parts solvent, yielding a tenfold dilution. This approach applies across laboratory workflows and is a common practical use of the unit.

Related units include micromolar (μM; 10^-6 M) and molarity (M).