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Magnesium is never sold as pure magnesium metal — it's always bonded to something else (glycine, citrate, oxide, and so on) to make it stable and absorbable. The label weight is the weight of that whole bonded molecule. Elemental magnesium — the part your body actually uses — is a fraction of it, and that fraction is fixed by basic chemistry (the molecular weight of magnesium relative to the whole compound), not by marketing.
This means two products both labelled "500mg" can deliver very different actual doses depending on the form. Some manufacturers already do this conversion for you and print the elemental amount directly — when they do, trust that number over this estimate.
| Form | ~% Elemental | 500mg compound → elemental |
|---|---|---|
| Oxide | 60% | ~300mg |
| Citrate | 16% | ~81mg |
| Malate | 15% | ~78mg |
| Glycinate | 14% | ~70mg |
| Chloride (hexahydrate) | 12% | ~60mg |
| Sulfate / Epsom salt (heptahydrate) | 10% | ~49mg |
| Taurate | 9% | ~44mg |
| Aspartate | 8% | ~42mg |
| L-Threonate | 8% | ~42mg |
Calculated from standard molecular/formula weights for each compound's most common commercial hydration state. Real products can vary slightly by manufacturer — this is an estimate for label literacy, not a substitute for a product's own Supplement Facts panel.
The adult RDA for magnesium is roughly 310–360mg/day for women and 400–420mg/day for men, depending on age — and that's total intake from food and supplements combined, not a supplement target on its own. Most people get meaningful magnesium from diet already (leafy greens, nuts, whole grains, legumes), which is worth factoring in before assuming a supplement needs to cover the whole RDA by itself.