Magnesium chloride is 12.0–25.5% magnesium by weight and glycinate 11.8–14.1%, so 200 mg of magnesium takes 780–1,670 mg of chloride or 1,420–1,690 mg of glycinate. Chloride's range runs from the hexahydrate (12.0%) to the anhydrous salt (25.5%); the hexahydrate carries less than half the magnesium per gram, and labels rarely say which is inside. Label counts come from the NIH Dietary Supplement Label Database (DSLD) snapshot of 2026-08-10; prices come from Amazon offers observed 2026-10-26 to 2026-11-02 and are compared only inside one salt.
Which to pick for what
At 400 mg of magnesium, chloride needs 3–5 size 00 capsules of salt alone and glycinate 4–5, by the formulas MgCl₂ and Mg(C₂H₄NO₂)₂ at 0.8 g/mL.
- Fewest capsules. For 200 mg of magnesium: 780–1,670 mg of chloride, 2–3 size 00 or 1–2 size 000 capsules, against 1,420–1,690 mg of glycinate, 2–3 size 00 or 2 size 000. For 400 mg: 1,570–3,340 mg of chloride, 3–5 size 00 or 2–4 size 000, against 2,840–3,380 mg of glycinate, 4–5 size 00 or 3–4 size 000. Counts assume salt alone at 0.8 g/mL: 730 mg per size 00, 1,100 mg per size 000.
- What labels declare. Median magnesium per serving on DSLD labels, snapshot 2026-08-10, chloride: 124 mg; glycinate: 238 mg. The 400 mg figures are a yardstick for comparing salts, not a serving.
- Lowest cost inside each salt. Ranked US price offers as of 2026-11-02, chloride: 0; glycinate: 17. 30 days at 400 mg a day from the cheapest ranked glycinate offer: $7.99. From the cheapest ranked chloride offer: not computed, no ranked offer as of 2026-11-02.
- What studies measured. One study in the site's PubMed-checked registry includes both salts, and it was done in rats; as of October 2026 none compared them in people.
- PMID 16548135 (2005): 80 magnesium-depleted rats each received one of ten salts, both of these included, traced with stable isotopes. Depletion itself raises absorption.
- PMID 1468087 (1992): 12 adults with normal blood magnesium spent a week each on a chloride solution, slow-release chloride tablets and gluconate tablets, 16 mmol (about 389 mg of magnesium) per dose; urinary, serum and white-cell magnesium were measured over 24 hours.
- PMID 11794633 (2001): four US commercial preparations, chloride among them, were given to volunteers, with bioavailability read as the rise in urinary magnesium.
- For glycinate: PMID 14596323 (2003; 46 adults, 300 mg a day, amino-acid chelate against citrate and oxide) and PMID 39770988 (2024; 40 adults, plasma magnesium over 6 hours after single doses).
Side by side
For 400 mg of magnesium, chloride takes 1,570–3,340 mg of compound and glycinate 2,840–3,380 mg; label counts are from the DSLD snapshot of 2026-08-10 and prices were observed 2026-10-26 to 2026-11-02.
| Measure | Magnesium chloride | Magnesium glycinate |
|---|---|---|
| Magnesium by weight | 12.0–25.5% | 11.8–14.1% |
| Compound for 400 mg of magnesium | 1,570–3,340 mg | 2,840–3,380 mg |
| Size 00 capsules for 400 mg (salt alone) | 3–5 | 4–5 |
| Most magnesium one size 000 capsule can hold | 132–281 mg | 130–155 mg |
| Labels in NIH DSLD naming the salt | 19 | 126 |
| Median magnesium per serving on those labels | 124 mg | 238 mg |
| Ranked US price offers | 0 | 17 |
| Lowest price per 100 mg of magnesium, within the salt | no ranked offer as of 2026-11-02 | $0.0666 |
Compound masses are rounded to the nearest 10 mg.
What to check on the label
In the DSLD snapshot of 2026-08-10, 10 of 19 chloride labels and 73 of 126 glycinate labels name that salt as the only magnesium source.
- Hexahydrate or anhydrous. A label that says only "magnesium chloride" could mean either. As compound weight, 1,000 mg of chloride holds 120–255 mg of magnesium.
- Magnesium or compound? Supplement Facts should state the magnesium itself, with the salt in brackets. "Magnesium Glycinate 400 mg" as compound weight holds 47–56 mg of magnesium.
- Per-capsule ceiling. One size 000 capsule holds at most 132–281 mg of magnesium as chloride alone and 130–155 mg as glycinate at 0.8 g/mL. The label audit lists labels above their capsule.
- "Buffered" glycinate. The word means an alkaline magnesium salt, usually oxide, is mixed in, and the label rarely says how much.
Where to go next
The glycinate ranking orders 17 ranked offers by price per 100 mg of magnesium, prices observed 2026-10-26 to 2026-11-02. Chloride gets a ranking page once it has 3 ranked offers; it has 0 as of 2026-11-02.