mmol = molecular weight (MW) in mg.

Magnesium is commercially available as magnesium sulfate heptahydrate with a molecular weight (MW) of 246.47mg.

Therefore 1 g magnesium sulfate (heptahydrate) is approximately equivalent to 4 mmol.

The difference between equivalents and moles is the number of charges the ion gives up or takes on. Magnesium has 2 charges. Therefore 4 mmol Mg (2+) is equivalent to 8 meq or 1g MgSO₄