Magnesium aspartate is 7.5–15.6% magnesium by weight and glycinate 11.8–14.1%, so 200 mg of magnesium takes 1,280–2,670 mg of aspartate or 1,420–1,690 mg of glycinate. Aspartate's range is wide because three compounds share the name: 1:1 magnesium aspartate (15.6%), magnesium bis(hydrogen aspartate) (8.4%) and its dihydrate (7.5%), and labels rarely say which. 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, aspartate needs 4–8 size 00 capsules of salt alone and glycinate 4–5, by the formulas MgC₄H₅NO₄ and Mg(C₂H₄NO₂)₂ at 0.8 g/mL.
- Fewest capsules. For 200 mg of magnesium: 1,280–2,670 mg of aspartate, 2–4 size 00 or 2–3 size 000 capsules, against 1,420–1,690 mg of glycinate, 2–3 size 00 or 2 size 000. For 400 mg: 2,560–5,340 mg of aspartate, 4–8 size 00 or 3–5 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, aspartate: 200 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, aspartate: 0; glycinate: 17. 30 days at 400 mg a day from the cheapest ranked glycinate offer: $7.99. From the cheapest ranked aspartate 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 11794633 (2001): four US commercial preparations, oxide, chloride, lactate and aspartate, were given to volunteers, and bioavailability was read as the rise in urinary magnesium. Small sample; urine stands in for absorption.
- 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, glycinate takes 2,840–3,380 mg of compound and aspartate 2,560–5,340 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 aspartate |
|---|---|---|
| Magnesium by weight | 11.8–14.1% | 7.5–15.6% |
| Compound for 400 mg of magnesium | 2,840–3,380 mg | 2,560–5,340 mg |
| Size 00 capsules for 400 mg (salt alone) | 4–5 | 4–8 |
| Most magnesium one size 000 capsule can hold | 130–155 mg | 82–172 mg |
| Labels in NIH DSLD naming the salt | 126 | 46 |
| Median magnesium per serving on those labels | 238 mg | 200 mg |
| Ranked US price offers | 17 | 0 |
| Lowest price per 100 mg of magnesium, within the salt | $0.0666 | no ranked offer as of 2026-11-02 |
Compound masses are rounded to the nearest 10 mg.
What to check on the label
In the DSLD snapshot of 2026-08-10, 25 of 46 aspartate labels and 73 of 126 glycinate labels name that salt as the only magnesium source.
- Which aspartate. Without the compound named, "magnesium aspartate" can carry anything from 7.5% to 15.6% magnesium by weight. As compound weight, 1,000 mg of it holds 75–156 mg of magnesium.
- Aspartic acid. Listed as its own ingredient, it is the free amino acid and adds no magnesium.
- Paired minerals. Labels that pair magnesium aspartate with potassium aspartate list two minerals; only the magnesium line counts toward magnesium.
- Per-capsule ceiling. One size 000 capsule holds at most 82–172 mg of magnesium as aspartate 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.
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. Aspartate gets a ranking page once it has 3 ranked offers; it has 0 as of 2026-11-02.