Enter the two numbers printed on any magnesium supplement label. This works out what share of the compound is actually magnesium, and tells you whether that figure is possible for a single ingredient or only for a blend.
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Enter both numbers
Magnesium content of common forms
| Form | Magnesium by weight | Note |
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How this is calculated. Magnesium bisglycinate is Mg(C2H4NO2)2, molar mass 172.42 g/mol against magnesium's 24.305 g/mol, giving 24.305 divided by 172.42 = 14.10%. That is a ceiling, not a grade: no lot of pure bisglycinate can exceed it, and hydrated commercial grades assay lower, around 11 to 13%. Magnesium oxide is MgO at 40.30 g/mol, giving 60.31%, the densest form in normal use. Where a result sits above 14.1% and the product is sold as glycinate, this page estimates the blend as bisglycinate plus magnesium oxide, the most common buffering pair, so the split shown is an estimate of composition rather than a measurement. Only a certificate of analysis, or a solubility, nitrogen or X-ray diffraction test, identifies the second source with certainty. A total-magnesium assay cannot, because digestion reduces every form to the same ion before it is measured.