How much elemental magnesium is in my supplement? The label math, explained
The front of the bottle says "1,500 mg". The back says 120 mg of magnesium. Both are true, and only one tells you how much magnesium you're getting. Here's how to read any magnesium label in about 60 seconds.
Elemental magnesium vs compound weight
Magnesium never comes on its own in a supplement. It's always bound to a "partner" molecule such as glycine, citrate, oxide, taurine or threonate. The compound weight is the magnesium plus its partner. The elemental magnesium is only the magnesium part.
The NIH Office of Dietary Supplements explains that the Supplement Facts panel "declares the amount of elemental magnesium in the product, not the weight of the entire magnesium-containing compound". Front labels are marketing, and they often show the bigger compound number.
A real label, line by line
This layout is copied from the Nutricost Magnesium Taurate label (brand page, checked 21 Oct 2026). The front of the bottle says "1,500 mg".
| Label line | What it says | What it means |
|---|---|---|
| Serving Size | 3 Capsules | One serving is 3 capsules, not 1 |
| Magnesium | 120 mg (29% DV) | The elemental magnesium per serving. This is the number to use. |
| Magnesium Taurate | 1,500 mg | The whole compound. Only about 8% of it is magnesium. |
| % DV | 29% | 120 mg ÷ the 420 mg Daily Value ≈ 29% |
So "1,500 mg" on the front is 120 mg of magnesium across 3 capsules. Threonate works the same way. Nutricost's Magtein label shows 144 mg of magnesium from 2,000 mg of magnesium L-threonate.
How much of each form is magnesium?
You can estimate elemental magnesium from the compound weight with one multiplication: real magnesium ≈ compound weight × the percentage below.
| Form | Share that is magnesium (approx.) | 1,000 mg of compound ≈ |
|---|---|---|
| Oxide | 60% | 603 mg magnesium |
| Hydroxide | 42% | 417 mg |
| Carbonate | 29% | 288 mg |
| Citrate (anhydrous) | 16% | 162 mg |
| Malate | 16% | 155 mg |
| Bisglycinate | 14% | 141 mg |
| Lactate (anhydrous) | 12% | 120 mg |
| Chloride (hexahydrate) | 12% | 120 mg |
| Sulfate (Epsom salt, 7H2O) | 10% | 99 mg |
| Taurate | 9% | 89 mg |
| L-Threonate | 7–8% | 72–83 mg |
Calculated from chemical formulas. Real products vary with water content: Magtein labels show 144 mg magnesium per 2,000 mg (7.2%).
Oxide's high percentage is why oxide products can print big magnesium numbers in small pills. In absorption studies, though, oxide was absorbed poorly: about 4% in one study (Firoz & Graber 2001) and no different from placebo for blood levels in another (Walker 2003). A high magnesium number doesn't tell you how much your body takes up.
The 60-second label check
- Find the serving size. Is the magnesium amount for 1 capsule or for 3?
- Find the "Magnesium" line on the Supplement Facts panel. That's the elemental amount. Ignore the front of the bottle.
- Read the brackets. "Magnesium (as magnesium glycinate and magnesium oxide)" means it's a blend, and the label has told you.
- If a compound weight is listed, divide. Magnesium mg ÷ compound mg. Pure bisglycinate should come out around 14%. Doctor's Best High Absorption lists 200 mg of magnesium from 2,000 mg of lysinate glycinate chelate. That's 10%, consistent with a real chelate. A "glycinate" at 25% or more probably contains something else.
- If no compound weight is listed, sanity-check the pill size. 400 mg of magnesium from pure bisglycinate needs about 2.8 g of powder. In 2 capsules, that's about 1.4 g each, which is very large. If the numbers don't fit, ask the brand.
The pill-size check is a rough plausibility test, not proof. Capsule fill weights vary, and only the manufacturer or a lab test can confirm a formula.
Decode every label you own
The free sample includes the label-math page and the "buffered glycinate" check. The full Magnesium Decoder adds a label decoder worksheet and an Excel tracker that flags labels that don't add up, plus 30 products already decoded.
Free 4-page sample (PDF, no email) See the Magnesium Decoder, $7
Magnesium forms on one page
How much of each form is actual magnesium (oxide ≈60%, citrate ≈16%, glycinate ≈14%, threonate ≈7–8%) and what the research says, in plain words. Free PDF. You also join the Renvo Life newsletter. We'll email you the link after you confirm.
Not medical advice.
Why this matters for price
Once you know the elemental amount, you can compare products fairly. $ per 100 mg = price ÷ (servings × mg magnesium per serving) × 100. On that basis, the Nutricost taurate above costs $0.21 per 100 mg and Nutricost's threonate $0.87, while budget citrate and glycinate capsules cost about 8 to 18 cents (brand store prices, checked 21 Oct 2026). See magnesium cost per dose compared for the full breakdown, the cost per 100 mg calculator for a bottle of your own, and glycinate vs citrate for how the two most popular forms compare.
FAQ
What does "elemental magnesium" mean?
The weight of the magnesium itself, without the molecule it's bound to. US Supplement Facts panels list it on the "Magnesium" line.
Why does the front of the bottle show a bigger number?
It's often the weight of the whole compound, for example 1,500 mg of magnesium taurate, which contains 120 mg of magnesium.
Is a higher percentage of magnesium better?
Not necessarily. Oxide is about 60% magnesium, but it was poorly absorbed in studies. The percentage tells you about pill size and label math, not absorption.
What if my label doesn't list a compound weight?
Use the pill-size sanity check, or ask the brand. Many labels give only the elemental amount.
How much magnesium should I take?
This page doesn't give dosing advice. Ask your doctor or pharmacist, especially if you have kidney problems or take other medicines.
Related: Magnesium glycinate vs citrate · Magnesium cost per dose compared · The Magnesium Decoder · All guides
More in this series: buffered glycinate check · threonate: what the price buys · premium vs budget · why oxide is cheapest per mg · shopping by the numbers
Sources: NIH Office of Dietary Supplements, Magnesium fact sheet for health professionals; Walker et al. 2003 (Magnesium Research); Firoz & Graber 2001 (Magnesium Research); brand web stores and the NIH Dietary Supplement Label Database, checked 21 Oct 2026. No brand paid to appear, and there are no affiliate links on this page.
Health disclaimer. Not medical advice. This is a shopping and label guide. It doesn't diagnose, treat or recommend doses, and makes no promises of results. Check with your doctor or pharmacist before starting a supplement, especially if you have kidney disease, are pregnant, or take prescription medicines.
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Last updated 30 Oct 2026