How to use the Magnesium Calculator
- 1 Choose the form of magnesium named on the product, such as magnesium glycinate.
- 2 Enter the weight of the compound per serving in mg and the number of servings per day.
- 3 See the elemental magnesium and how the daily amount compares with the supplement upper limit.
500 mg magnesium citrate is not 500 mg magnesium
Magnesium supplements contain a magnesium compound. Only part of its weight is magnesium; the rest is the molecule it is bound to. That is why 500 mg of magnesium citrate provides about 81 mg of elemental magnesium, while 500 mg of magnesium oxide provides about 302 mg. Reference intakes and upper limits always refer to elemental magnesium.
Elemental magnesium by form
| Form | Elemental magnesium | In 500 mg |
|---|---|---|
| Magnesium oxide | 60.3% | 302 mg |
| Magnesium hydroxide | 41.7% | 208 mg |
| Magnesium carbonate | 28.8% | 144 mg |
| Magnesium citrate | 16.2% | 81 mg |
| Magnesium malate | 15.5% | 78 mg |
| Magnesium glycinate (bisglycinate) | 14.1% | 71 mg |
| Magnesium chloride (hexahydrate) | 12.0% | 60 mg |
| Magnesium lactate (dihydrate) | 10.2% | 51 mg |
| Magnesium sulfate (Epsom salt) | 9.9% | 49 mg |
| Magnesium taurate | 8.9% | 45 mg |
| Magnesium L-threonate | 8.3% | 41 mg |
Values are calculated from the chemical formulas. Some products use buffered or partially reacted forms, so check whether the label also states the elemental amount, often written as “magnesium (as glycinate) 100 mg”.
How much magnesium is enough – and too much?
The US RDA is 400–420 mg for men and 310–320 mg for women; EFSA sets an Adequate Intake of 350 mg for men and 300 mg for women. These amounts come mostly from food such as nuts, seeds, whole grains, legumes and green vegetables.
The upper limit applies only to supplemental magnesium: 350 mg per day in the US and 250 mg per day in the EU. Above these amounts, diarrhoea and stomach cramps become more likely, particularly with magnesium oxide, citrate and chloride. People with reduced kidney function should only take magnesium supplements on medical advice.
Forms and absorption
The form affects how much magnesium a tablet contains and how well it dissolves. Organic salts such as citrate and glycinate tend to be absorbed better than oxide, but provide less magnesium per gram, so you need a larger tablet for the same elemental dose.
Sources
Frequently asked questions
How much elemental magnesium is in magnesium glycinate?
Magnesium bisglycinate is about 14% magnesium, so 1,000 mg provides roughly 141 mg of elemental magnesium.
Is 400 mg of magnesium too much?
400 mg of elemental magnesium from supplements is above both the US (350 mg) and EU (250 mg) supplement upper limits. Magnesium from food does not count towards the limit.
Which magnesium form contains the most magnesium?
Magnesium oxide, at about 60% elemental magnesium, followed by hydroxide and carbonate.
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