mg ↔ mmol converter
mg ↔ mmol and µg ↔ µmol using the compound's molar mass.
Must be greater than zero. 1 mmol weighs the molar weight in mg.
Pick the unit you have, enter the value and the molar weight — mg, µg, mmol, and µmol all appear here.
Formula and how to use it
Mass and amount of substance are related by the molar mass MW: amount in mmol = mass in mg ÷ MW (g/mol), because a millimole of a compound weighs MW milligrams. The micro pair follows the same rule: µmol = µg ÷ MW, since a micromole weighs MW micrograms. The two scales differ by a clean factor of 1,000 (1 mmol = 1,000 µmol and 1 mg = 1,000 µg).
Worked example: glucose has MW 180.156 g/mol, so 1 mmol weighs 180.156 mg and 500 mg of glucose is 500 ÷ 180.156 = 2.78 mmol. Likewise, 90 µg of a drug with MW 300 g/mol is 90 ÷ 300 = 0.30 µmol. The molar mass works for both scales — only the prefixes change.
Enter any one of mg, µg, mmol, or µmol together with the molar mass and this calculator reports all four. The molar mass must be greater than zero. The same arithmetic underlies dosing, reagent preparation, and assay calculations, and is shared with the compound pages where the molar mass is pre-filled.