millimólL

MillimólL, usually written as mmol/L, is a unit of concentration in the metric system. It expresses the amount of substance in millimoles per liter of solution. Because one millimole equals 10^-3 moles, 1 mmol/L is equal to 0.001 mol/L, and 1 mol/L equals 1000 mmol/L. It is also related to 1000 µmol/L, since 1 mmol/L = 1000 µmol/L.

The unit is commonly used to describe molarity in chemistry, biology, and medicine. In clinical chemistry, many blood and urine measurements are reported in mmol/L, especially electrolytes such as sodium, potassium, and chloride. For example, typical sodium levels are stated in the range of about 135–145 mmol/L, and potassium in roughly 3.5–5.0 mmol/L. Millimolar concentrations can be converted to other mass-based or unit-based expressions using the solute’s molar mass: the mass concentration in mg/L equals the mmol/L value times the solute’s molar mass in g/mol.

Practical use: to prepare a solution with a desired mmol/L concentration, one multiplies the target concentration (mmol/L) by the solution volume (liters) to obtain the required amount of substance in millimoles. Then the substance is weighed and dissolved to the specified volume.

Relation to other units: mmol/L is a specific instance of molarity (mol/L) with a milli prefix. It is distinct from micromolar (µmol/L) and from mass concentration units such as mg/L, which depend on molar mass.