Magnesium Label Checker: How Much Magnesium Are You Really Getting?

Most of the weight of a magnesium supplement isn't magnesium. In glycinate, magnesium is only about 14% of the compound, so "1,000 mg magnesium glycinate" on the front of a bottle can mean about 140 mg of actual magnesium. This checker converts the compound amount into the number that matters: elemental magnesium.

Which number is on your label?

Labels show magnesium in one of two ways, and the checker is only needed for one of them.

1. The Supplement Facts panel. In the US, the panel on the back has to list the amount of magnesium itself. A line like "Magnesium (as magnesium bisglycinate) 200 mg" means 200 mg of elemental magnesium. That's your dose. You don't need to convert it.
2. The front of the bottle, or an ingredient list. "Magnesium Glycinate 1,000 mg" usually means the weight of the whole compound, magnesium plus glycine. That's the number to put into the checker.

If the front of the bottle and the back panel disagree, the back panel wins. Our guide to magnesium glycinate has an example label with the right line marked.

How much magnesium is in each form

These are worked out from the molecular weight of each pure compound. Real ingredients can differ by a point or two, because of water bound into the powder or a little of another form mixed in. That's close enough to tell you whether a product gives you 100 mg or 300 mg, which is the question that matters.

Oxide looks like the best deal on this table and isn't. It packs the most magnesium into each capsule, but your body absorbs much less of it than citrate, glycinate and the other organic forms. In one well-known study only about 4% of it was absorbed, and a 2021 review found the same pattern. It's also the form most likely to loosen your stools. The comparison of glycinate, citrate and the other forms goes into which to choose.

What to do with your result

• Under about 100 mg a day: probably too little to make a difference, unless your diet is already close to the daily need.
• 200 to 350 mg a day: the range most people take, and what the trials used. The 2025 sleep trial gave 250 mg (see our sleep guide).
• Over 350 mg a day: above the upper limit the NIH sets for magnesium from supplements. Magnesium from food doesn't count toward that limit (NIH Office of Dietary Supplements). Ask your doctor before going higher.

The "daily need" line compares your result with the recommended intake of 320 mg for women and 420 mg for men aged 31 and over. That target includes food, so a supplement doesn't need to cover it on its own.

One more thing to check: "buffered"

Some glycinate products mix in magnesium oxide to fit more magnesium into each capsule. If you see oxide in the ingredient list, the checker will undercount, because part of the magnesium comes from a different form. It also means the product is more likely to upset your stomach. Look for "fully reacted" or "100% chelated" if you want pure glycinate.

Who should check with a doctor first

Anyone with kidney disease, because your kidneys clear extra magnesium. And anyone taking antibiotics (tetracyclines or quinolones), osteoporosis drugs (bisphosphonates), diuretics or acid-reflux medication, since magnesium can change how these work. More on that in our magnesium glycinate guide.

Questions people ask

How much elemental magnesium is in 500 mg of magnesium glycinate?

About 70 mg. Magnesium makes up roughly 14% of magnesium glycinate by weight, so 500 mg of the compound gives you about 70 mg of magnesium.

Is the magnesium amount on the Supplement Facts panel elemental?

Yes. On US labels, the amount listed next to Magnesium on the Supplement Facts panel is elemental magnesium, the number to dose by. The front of the bottle often shows the whole compound instead.

Why does magnesium oxide have so much magnesium?

Oxygen is a very light partner, so about 60% of magnesium oxide is magnesium. But much less of it is absorbed than from citrate or glycinate, and it's more likely to cause diarrhea.

TD

Written by Tom D

Tom has trained in the gym for years and has taken 5 g of creatine every day for about a decade, with magnesium on and off for most of the year. Reading the research behind supplements started as a hobby; this site is where he writes it up. He isn't a doctor or dietitian, so every claim links to the study behind it.

Sources

1. NIH Office of Dietary Supplements, Magnesium fact sheet
2. Firoz & Graber 2001, Bioavailability of US commercial magnesium preparations
3. Systematic review: bioavailability of magnesium food supplements (2021)

We link to the original study wherever we can. Read how we grade evidence and choose products.