Same elemental magnesium · two salts · snapshot 2026-08-10
Magnesium carbonate vs oxide: 694–807 vs 332 mg of compound for 200 mg of magnesium
Magnesium carbonate is 24.8–28.8% elemental magnesium and magnesium oxide is 60.3%, so 200 mg of magnesium needs 694–807 mg of carbonate against 332 mg of oxide: 1–2 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 carbonate alone, against 0 of 12 for oxide. Prices within each salt: no ranked carbonate 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 · carbonate 347–404 |
| 200 mg magnesium |
| oxide 332 · carbonate 694–807 |
| 400 mg magnesium |
| oxide 663 · carbonate 1,387–1,614 |
Data release 2026-08-10-f441aa9f · registry snapshot 2026-08-10 · latest price observation 2026-11-02 · chemistry 2026-10-17
How much carbonate or oxide carries the same elemental magnesium?
At the same elemental amount, oxide (60.3% magnesium) always needs less compound than carbonate (24.8–28.8%): for 400 mg of magnesium, 663 mg against 1,387–1,614 mg. That is the mass of powder per dose; how much of it is absorbed is what the studies below measured.
computed| Elemental magnesium | carbonate compound | carbonate size 00 | oxide compound | oxide size 00 |
|---|---|---|---|---|
| 100 mg | 347–404 mg | 1 | 166 mg | 1 |
| 200 mg | 694–807 mg | 1–2 | 332 mg | 1 |
| 400 mg | 1,387–1,614 mg | 2–3 | 663 mg | 1 |
carbonate: anhydrous or hydrated; labels rarely state which; hydration ambiguity stays a range.
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 carbonate 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 |
|---|---|---|---|---|
| carbonate | 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 carbonate 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 |
|---|---|---|---|---|
| carbonate | 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 carbonate and oxide side by side?
2 studies in the PubMed-checked registry measured both salts in the same design; 2 involve carbonate and 12 involve oxide in total. They measured outcomes of the salts, not of any label.
measured| Year | Study | Salts measured | PubMed |
|---|---|---|---|
| 2022 | Effects of short-term magnesium supplementation on ionized, total magnesium and other relevant electrolytes levels. | oxide, citrate, carbonate | 35041150 |
| 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 |
| 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 |
| 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 |
| 2003 | Mg citrate found more bioavailable than other Mg preparations in a randomised, double-blind study | citrate, oxide, glycinate | 14596323 |
4 additional rows
| Year | Study | Salts measured | PubMed |
|---|---|---|---|
| 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 carbonate and oxide?
No label names both carbonate and oxide as of 2026-08-10, against 23 labels naming carbonate 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 | carbonate compound | carbonate size 00 | oxide compound | oxide size 00 |
|---|---|---|---|---|
| 25 mg | 87–101 mg | 1 | 41 mg | 1 |
| 50 mg | 173–202 mg | 1 | 83 mg | 1 |
| 75 mg | 260–303 mg | 1 | 124 mg | 1 |
| 100 mg | 347–404 mg | 1 | 166 mg | 1 |
| 125 mg | 434–504 mg | 1 | 207 mg | 1 |
| 150 mg | 520–605 mg | 1 | 249 mg | 1 |
| 175 mg | 607–706 mg | 1 | 290 mg | 1 |
| 200 mg | 694–807 mg | 1–2 | 332 mg | 1 |
32 additional rows
| Elemental magnesium | carbonate compound | carbonate size 00 | oxide compound | oxide size 00 |
|---|---|---|---|---|
| 225 mg | 780–908 mg | 2 | 373 mg | 1 |
| 250 mg | 867–1,009 mg | 2 | 414 mg | 1 |
| 275 mg | 954–1,110 mg | 2 | 456 mg | 1 |
| 300 mg | 1,041–1,211 mg | 2 | 497 mg | 1 |
| 325 mg | 1,127–1,312 mg | 2 | 539 mg | 1 |
| 350 mg | 1,214–1,412 mg | 2 | 580 mg | 1 |
| 375 mg | 1,301–1,513 mg | 2–3 | 622 mg | 1 |
| 400 mg | 1,387–1,614 mg | 2–3 | 663 mg | 1 |
| 425 mg | 1,474–1,715 mg | 3 | 705 mg | 1 |
| 450 mg | 1,561–1,816 mg | 3 | 746 mg | 2 |
| 475 mg | 1,648–1,917 mg | 3 | 787 mg | 2 |
| 500 mg | 1,734–2,018 mg | 3 | 829 mg | 2 |
| 525 mg | 1,821–2,119 mg | 3 | 870 mg | 2 |
| 550 mg | 1,908–2,220 mg | 3–4 | 912 mg | 2 |
| 575 mg | 1,994–2,320 mg | 3–4 | 953 mg | 2 |
| 600 mg | 2,081–2,421 mg | 3–4 | 995 mg | 2 |
| 625 mg | 2,168–2,522 mg | 3–4 | 1,036 mg | 2 |
| 650 mg | 2,255–2,623 mg | 4 | 1,078 mg | 2 |
| 675 mg | 2,341–2,724 mg | 4 | 1,119 mg | 2 |
| 700 mg | 2,428–2,825 mg | 4 | 1,160 mg | 2 |
| 725 mg | 2,515–2,926 mg | 4–5 | 1,202 mg | 2 |
| 750 mg | 2,601–3,027 mg | 4–5 | 1,243 mg | 2 |
| 775 mg | 2,688–3,128 mg | 4–5 | 1,285 mg | 2 |
| 800 mg | 2,775–3,228 mg | 4–5 | 1,326 mg | 2 |
| 825 mg | 2,862–3,329 mg | 4–5 | 1,368 mg | 2 |
| 850 mg | 2,948–3,430 mg | 5 | 1,409 mg | 2 |
| 875 mg | 3,035–3,531 mg | 5 | 1,451 mg | 2 |
| 900 mg | 3,122–3,632 mg | 5 | 1,492 mg | 3 |
| 925 mg | 3,208–3,733 mg | 5–6 | 1,533 mg | 3 |
| 950 mg | 3,295–3,834 mg | 5–6 | 1,575 mg | 3 |
| 975 mg | 3,382–3,935 mg | 5–6 | 1,616 mg | 3 |
| 1,000 mg | 3,469–4,036 mg | 5–6 | 1,658 mg | 3 |
Source · Chemical formulas and NIH DSLD labels · snapshot 2026-08-10 · release 2026-08-10-f441aa9f · CSV · method