Same elemental magnesium · two salts · snapshot 2026-08-10
Magnesium hydroxide vs oxide: 480 vs 332 mg of compound for 200 mg of magnesium
Magnesium hydroxide is 41.7% elemental magnesium and magnesium oxide is 60.3%, so 200 mg of magnesium needs 480 mg of hydroxide against 332 mg of oxide: 1 vs 1 size 00 capsules at powder density 0.8 g/mL, the top of the usual 0.6–0.8 range. No capsule label names hydroxide alone, against 0 of 12 for oxide. Prices within each salt: no ranked hydroxide price; oxide from $0.0148 per 100 mg (median $0.0293, 5 ranked offers); observed 2026-10-26 to 2026-11-02.
computed from chemical formulas
Chart data
| Displayed chart text |
|---|
| 100 mg magnesium |
| oxide 166 · hydroxide 240 |
| 200 mg magnesium |
| oxide 332 · hydroxide 480 |
| 400 mg magnesium |
| oxide 663 · hydroxide 960 |
Data release 2026-08-10-f441aa9f · registry snapshot 2026-08-10 · latest price observation 2026-11-02 · chemistry 2026-10-17
How much hydroxide or oxide carries the same elemental magnesium?
At the same elemental amount, oxide (60.3% magnesium) always needs less compound than hydroxide (41.7%): for 400 mg of magnesium, 663 mg against 960 mg. That is the mass of powder per dose; how much of it is absorbed is what the studies below measured.
computed| Elemental magnesium | hydroxide compound | hydroxide size 00 | oxide compound | oxide size 00 |
|---|---|---|---|---|
| 100 mg | 240 mg | 1 | 166 mg | 1 |
| 200 mg | 480 mg | 1 | 332 mg | 1 |
| 400 mg | 960 mg | 2 | 663 mg | 1 |
Source · Chemical formulas and NIH DSLD labels · snapshot 2026-08-10 · release 2026-08-10-f441aa9f · CSV · method
Estimated salt mass versus assumed capsule capacity
No capsule label names hydroxide alone, against 0 of 12 for oxide. Verdicts use the most favourable hydration and the most units per serving at powder density 0.8 g/mL, the top of the usual 0.6–0.8 range; the audited registry as a whole has 8 of 137 capsule labels above size 000.
computed with assumption| Salt | Audited capsule labels | Fits 0 or 00 | Needs 000 | Exceeds 000 |
|---|---|---|---|---|
| hydroxide | 0 | 0 | 0 | 0 |
| oxide | 12 | 11 | 1 | 0 |
Source · NIH DSLD labels; mass balance · recognized salt only; snapshot 2026-08-10 · release 2026-08-10-f441aa9f · CSV · method
What does each cost per 100 mg of elemental magnesium, within its own salt?
Compared only with offers of the same salt: no ranked hydroxide price; oxide from $0.0148 per 100 mg (median $0.0293, 5 ranked offers). Prices observed 2026-10-26 to 2026-11-02; a ranking exists only inside one salt, because the compound mass per 100 mg of magnesium differs between salts.
computed| Salt | Ranked offers | Lowest per 100 mg | Median per 100 mg | Observed |
|---|---|---|---|---|
| hydroxide | 0 | none | none | 2026-11-02 |
| oxide | 5 | $0.0148 | $0.0293 | 2026-11-02 |
Source · Amazon via licensed data provider; NIH DSLD · unique ASIN × date; prices observed 2026-10-26 to 2026-11-02 · release 2026-08-10-f441aa9f · CSV · method
Has any study measured hydroxide and oxide side by side?
No study in the PubMed-checked registry measured hydroxide and oxide side by side as of 2026-08-10; 1 involve hydroxide and 12 involve oxide separately.
measured| Year | Study | Salts measured | PubMed |
|---|---|---|---|
| 2025 | Comparing the Bioavailability of Two Seawater-Derived Magnesium Preparations. | citrate, hydroxide | 40955524 |
| 2026 | Randomized, open-label study of the short-term pharmacokinetics of oral magnesium oxide in healthy volunteers. | oxide | 42091979 |
| 2024 | Comparative Clinical Study on Magnesium Absorption and Side Effects After Oral Intake of Microencapsulated Magnesium (MAGSHAPE™ Microcapsules) Versus Other Magnesium Sources. | citrate, glycinate, oxide | 39770988 |
| 2022 | Effects of short-term magnesium supplementation on ionized, total magnesium and other relevant electrolytes levels. | oxide, citrate, carbonate | 35041150 |
| 2020 | Dose-Dependent Absorption Profile of Different Magnesium Compounds | oxide, citrate, glycinate, malate | 30761462 |
| 2019 | Timeline (Bioavailability) of Magnesium Compounds in Hours: Which Magnesium Compound Works Best? | sulfate, oxide, taurate, citrate, malate | 29679349 |
| 2012 | Comparison of magnesium status using X-ray dispersion analysis following magnesium oxide and magnesium citrate treatment of healthy subjects | citrate, oxide | 22433473 |
| 2005 | Study of magnesium bioavailability from ten organic and inorganic Mg salts in Mg-depleted rats using a stable isotope approach | oxide, chloride, sulfate, carbonate, citrate, gluconate, lactate, aspartate, glycinate | 16548135 |
5 additional rows
| Year | Study | Salts measured | PubMed |
|---|---|---|---|
| 2003 | Mg citrate found more bioavailable than other Mg preparations in a randomised, double-blind study | citrate, oxide, glycinate | 14596323 |
| 2001 | Bioavailability of US commercial magnesium preparations | oxide, chloride, lactate, aspartate | 11794633 |
| 1995 | Bioavailability of magnesium diglycinate vs magnesium oxide in patients with ileal resection | glycinate, oxide | 7815675 |
| 1990 | Magnesium bioavailability from magnesium citrate and magnesium oxide | citrate, oxide | 2407766 |
| 1990 | Effect of magnesium citrate and magnesium oxide on the crystallization of calcium salts in urine | citrate, oxide | 2299712 |
Source · PubMed-checked study registry · registry checked 2026-08-10 · release 2026-08-10-f441aa9f · CSV · method
How many labels name both hydroxide and oxide?
No label names both hydroxide and oxide as of 2026-08-10, against 10 labels naming hydroxide and 124 naming oxide.
measured| Label | Declared elemental per serving | NIH DSLD |
|---|---|---|
| No label as of 2026-08-10 |
Source · Chemical formulas and NIH DSLD labels · snapshot 2026-08-10 · release 2026-08-10-f441aa9f · CSV · method
What does every dose from 25 to 1,000 mg of magnesium need in each salt?
The table converts 40 elemental amounts, 25 to 1,000 mg in 25 mg steps, into compound mass and size 00 capsules for both salts, against 730 mg per size 00 capsule at powder density 0.8 g/mL, the top of the usual 0.6–0.8 range. The first eight rows are shown; the rest open below.
computed| Elemental magnesium | hydroxide compound | hydroxide size 00 | oxide compound | oxide size 00 |
|---|---|---|---|---|
| 25 mg | 60 mg | 1 | 41 mg | 1 |
| 50 mg | 120 mg | 1 | 83 mg | 1 |
| 75 mg | 180 mg | 1 | 124 mg | 1 |
| 100 mg | 240 mg | 1 | 166 mg | 1 |
| 125 mg | 300 mg | 1 | 207 mg | 1 |
| 150 mg | 360 mg | 1 | 249 mg | 1 |
| 175 mg | 420 mg | 1 | 290 mg | 1 |
| 200 mg | 480 mg | 1 | 332 mg | 1 |
32 additional rows
| Elemental magnesium | hydroxide compound | hydroxide size 00 | oxide compound | oxide size 00 |
|---|---|---|---|---|
| 225 mg | 540 mg | 1 | 373 mg | 1 |
| 250 mg | 600 mg | 1 | 414 mg | 1 |
| 275 mg | 660 mg | 1 | 456 mg | 1 |
| 300 mg | 720 mg | 1 | 497 mg | 1 |
| 325 mg | 780 mg | 2 | 539 mg | 1 |
| 350 mg | 840 mg | 2 | 580 mg | 1 |
| 375 mg | 900 mg | 2 | 622 mg | 1 |
| 400 mg | 960 mg | 2 | 663 mg | 1 |
| 425 mg | 1,020 mg | 2 | 705 mg | 1 |
| 450 mg | 1,080 mg | 2 | 746 mg | 2 |
| 475 mg | 1,140 mg | 2 | 787 mg | 2 |
| 500 mg | 1,200 mg | 2 | 829 mg | 2 |
| 525 mg | 1,260 mg | 2 | 870 mg | 2 |
| 550 mg | 1,320 mg | 2 | 912 mg | 2 |
| 575 mg | 1,380 mg | 2 | 953 mg | 2 |
| 600 mg | 1,440 mg | 2 | 995 mg | 2 |
| 625 mg | 1,500 mg | 3 | 1,036 mg | 2 |
| 650 mg | 1,560 mg | 3 | 1,078 mg | 2 |
| 675 mg | 1,619 mg | 3 | 1,119 mg | 2 |
| 700 mg | 1,679 mg | 3 | 1,160 mg | 2 |
| 725 mg | 1,739 mg | 3 | 1,202 mg | 2 |
| 750 mg | 1,799 mg | 3 | 1,243 mg | 2 |
| 775 mg | 1,859 mg | 3 | 1,285 mg | 2 |
| 800 mg | 1,919 mg | 3 | 1,326 mg | 2 |
| 825 mg | 1,979 mg | 3 | 1,368 mg | 2 |
| 850 mg | 2,039 mg | 3 | 1,409 mg | 2 |
| 875 mg | 2,099 mg | 3 | 1,451 mg | 2 |
| 900 mg | 2,159 mg | 3 | 1,492 mg | 3 |
| 925 mg | 2,219 mg | 4 | 1,533 mg | 3 |
| 950 mg | 2,279 mg | 4 | 1,575 mg | 3 |
| 975 mg | 2,339 mg | 4 | 1,616 mg | 3 |
| 1,000 mg | 2,399 mg | 4 | 1,658 mg | 3 |
Source · Chemical formulas and NIH DSLD labels · snapshot 2026-08-10 · release 2026-08-10-f441aa9f · CSV · method