Millimolar (mM) is a unit of concentration equal to one millimole of a substance per litre of solution (mmol/L). A millimole is one-thousandth (1/1000) of a mole, making millimolar a convenient unit for describing the concentrations commonly encountered in plant physiology, soil chemistry, and laboratory experiments.
Researchers frequently use millimolar concentrations when studying nutrient uptake, enzyme activity, plant hormones, salinity stress, and silicon transport. For example, a nutrient solution containing 1 mM potassium contains one millimole of potassium ions per litre of solution.
Because a mole represents a specific number of molecules or ions rather than a weight, the mass represented by 1 mM varies depending on the substance. One millimolar calcium contains a different mass per litre than one millimolar silicon or nitrogen because their atomic weights differ.
Millimolar concentrations are larger than micromolar (µM) concentrations and smaller than molar (M) concentrations. One millimolar equals 1,000 micromolar and 0.001 molar.
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