Converting milligrams per liter (mg/L) to millimoles per liter (mmol/L) establishes the molecular weight of a substance in a liter. A gram (g) measures the absolute weight of a mass. A milligram is a measurement unit that represents 1/1000 of 1g. Thus, 1000mg are in 1g. A mole measures the amount of a substance or chemical in a mass. Conversely, 1mmol represents 1/1000 of 1 mole. Thus, 1000mmol are in 1 mole. Converting milligrams per liter (mg/L) into millimoles per liter requires completing a calculation based on the information you have for total milligrams and the molecular weight of the subject chemical.

Find the specific molecular weight, or moles, of your substance. For example, the molecular weight of blood sugar, or glucose, is 180.15588g/mol. A molecular weight calculator is linked in the Resources section.

Convert moles to millimoles. The conversion equation is 1(molecular weight)/ 1000 = mmol. Many diabetics use this equation to understand the milligrams to millimoles factor for glucose measurement. With the weight of glucose added, the equation is 1(180.15588)/1000 = 0.18015588mmol.

Convert millimoles to grams per unit. The equation for the calculation using glucose is 0.001mg/0.18015588 = 0.0055074 moles in each gram of the preferred liquid.

Place the numbers in the primary equation, and plug in your numbers. The equation is mg/L x (moles per gram of requested chemical) = mmol/L.

The final equation to convert milligrams per liter to millimoles per liter, using the information found for glucose, is 1mg/L x (0.0055074) = mmol/L.
Warnings
Use the correct units of measurement in calculations.