Magnesium L-threonate is 8.3% magnesium by weight and glycinate 11.8–14.1%, so 400 mg of magnesium takes 4,850 mg of threonate, seven size 00 capsules, or 2,840–3,380 mg of glycinate, four to five. Magtein is the trade name of magnesium L-threonate, and this site reads it as threonate. 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, threonate needs 7 size 00 capsules of salt alone and glycinate 4–5, by the formulas Mg(C₄H₇O₅)₂ and Mg(C₂H₄NO₂)₂ at 0.8 g/mL.
- Fewest capsules. For 200 mg of magnesium: 2,420 mg of threonate, 4 size 00 or 3 size 000 capsules, against 1,420–1,690 mg of glycinate, 2–3 size 00 or 2 size 000. For 400 mg: 4,850 mg of threonate, 7 size 00 or 5 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, threonate: 144 mg; glycinate: 238 mg. The 400 mg figures on this page are a yardstick for comparing salts, not a serving.
- Lowest cost inside each salt. 30 days at 400 mg a day from the cheapest ranked threonate offer: $138.86. From the cheapest ranked glycinate offer: $7.99. Ranked offers behind each figure, as of 2026-11-02, threonate: 1; glycinate: 17. The two are within-salt figures, not a ranking of the salts.
- What studies measured. As of October 2026, no study in the site's PubMed-checked registry measured L-threonate, and none compared it with glycinate. For glycinate, the registry holds:
- PMID 14596323 (2003): 46 adults took 300 mg of magnesium a day as an amino-acid chelate, citrate or oxide; bioavailability was compared at that equal dose.
- PMID 39770988 (2024): 40 women and men took single doses of bisglycinate, citrate, oxide and a microencapsulated form; plasma magnesium was measured over 6 hours.
- PMID 7815675 (1995): diglycinate against oxide in patients after ileal resection, a group with poor absorption to begin with.
Side by side
For 400 mg of magnesium, glycinate takes 2,840–3,380 mg of compound and threonate 4,850 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 glycinate | Magnesium L-threonate |
|---|---|---|
| Magnesium by weight | 11.8–14.1% | 8.3% |
| Compound for 400 mg of magnesium | 2,840–3,380 mg | 4,850 mg |
| Size 00 capsules for 400 mg (salt alone) | 4–5 | 7 |
| Most magnesium one size 000 capsule can hold | 130–155 mg | 91 mg |
| Labels in NIH DSLD naming the salt | 126 | 9 |
| Median magnesium per serving on those labels | 238 mg | 144 mg |
| Ranked US price offers | 17 | 1 |
| Lowest price per 100 mg of magnesium, within the salt | $0.0666 | $1.1572 |
Compound masses are rounded to the nearest 10 mg.
What to check on the label
In the DSLD snapshot of 2026-08-10, 8 of 9 threonate labels and 73 of 126 glycinate labels name that salt as the only magnesium source.
- Magnesium or compound? Supplement Facts should state the magnesium itself, with the salt in brackets. A large front-label figure for threonate can be compound weight: by the formula, 1,000 mg of magnesium L-threonate holds 83 mg of magnesium.
- Per-capsule ceiling. One size 000 capsule holds at most 91 mg of magnesium as threonate alone at 0.8 g/mL, and a size 00 about 60 mg. A threonate capsule declaring more cannot be threonate alone; the label audit lists labels like that.
- Magtein. The trade name on a label means magnesium L-threonate, and the 8.3% figure applies.
- "Buffered" glycinate. The word means an alkaline magnesium salt, usually oxide, is mixed in. This site keeps such labels out of single-salt counts.
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. Threonate gets a ranking page once it has 3 ranked offers; it has 1 as of 2026-11-02.