Same elemental magnesium · two salts · snapshot 2026-08-10

Magnesium hydroxide vs sulfate: 480 vs 991–2,028 mg of compound for 200 mg of magnesium

Magnesium hydroxide is 41.7% elemental magnesium and magnesium sulfate is 9.9–20.2%, so 200 mg of magnesium needs 480 mg of hydroxide against 991–2,028 mg of sulfate: 1 vs 2–3 size 00 capsules at powder density 0.8 g/mL, the top of the usual 0.6–0.8 range. No capsule label names either salt alone as of 2026-08-10, so no capsule verdict is counted. Neither salt has a ranked US retail price as of 2026-11-02.

computed from chemical formulas

hydroxide for 200 mg Mg480 mg41.7% magnesium · 1 size 00

sulfate for 200 mg Mg991–2,028 mg9.9–20.2% magnesium · 2–3 size 00

Exceeds size 000none · nonehydroxide · sulfate capsule labels

Cheapest by declared elemental magnesium, per 100 mg, within each salthydroxide none · sulfate none0 and 0 ranked offers · 2026-11-02

Compound mass for the same elemental magnesium: dark dot hydroxide (41.7%), grey dot sulfate (9.9–20.2%, upper mass bound); the labels give each salt's full range.

Chart data

Chart labels and values for the main chart
Displayed chart text
100 mg magnesium
hydroxide 240 · sulfate 495–1,014
200 mg magnesium
hydroxide 480 · sulfate 991–2,028
400 mg magnesium
hydroxide 960 · sulfate 1,981–4,057

Data release 2026-08-10-f441aa9f · registry snapshot 2026-08-10 · latest price observation 2026-11-02 · chemistry 2026-10-17

Elemental: The magnesium itself; the rest of the compound weight is the partner molecule.

Compound: The whole salt that must physically fit in a capsule; a lower magnesium fraction means more compound for the same magnesium.

How much hydroxide or sulfate carries the same elemental magnesium?

At the same elemental amount, hydroxide (41.7% magnesium) always needs less compound than sulfate (9.9–20.2%): for 400 mg of magnesium, 960 mg against 1,981–4,057 mg. That is the mass of powder per dose; how much of it is absorbed is what the studies below measured.

computed

Compound mass and size 00 capsules for hydroxide and sulfate
Elemental magnesium	hydroxide compound	hydroxide size 00	sulfate compound	sulfate size 00
100 mg	240 mg	1	495–1,014 mg	1–2
200 mg	480 mg	1	991–2,028 mg	2–3
400 mg	960 mg	2	1,981–4,057 mg	3–6

sulfate: anhydrous 20.2%, heptahydrate 9.9%; 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 either salt alone as of 2026-08-10, so no capsule verdict is counted. 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

Capsule verdicts for hydroxide and sulfate labels
Salt	Audited capsule labels	Fits 0 or 00	Needs 000	Exceeds 000
hydroxide	0	0	0	0
sulfate	0	0	0	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?

No ranked US retail price is matched for either salt as of 2026-11-02.

computed

Price per 100 mg of declared elemental magnesium, within each salt
Salt	Ranked offers	Lowest per 100 mg	Median per 100 mg	Observed
hydroxide	0	none	none	2026-11-02
sulfate	0	none	none	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 sulfate side by side?

No study in the PubMed-checked registry measured hydroxide and sulfate side by side as of 2026-08-10; 1 involve hydroxide and 2 involve sulfate separately.

measured

Registry studies involving hydroxide or sulfate
Year	Study	Salts measured	PubMed
2025	Comparing the Bioavailability of Two Seawater-Derived Magnesium Preparations.	citrate, hydroxide	40955524
2019	Timeline (Bioavailability) of Magnesium Compounds in Hours: Which Magnesium Compound Works Best?	sulfate, oxide, taurate, citrate, malate	29679349
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

Source · PubMed-checked study registry · registry checked 2026-08-10 · release 2026-08-10-f441aa9f · CSV · method

How many labels name both hydroxide and sulfate?

No label names both hydroxide and sulfate as of 2026-08-10, against 10 labels naming hydroxide and 4 naming sulfate.

measured

Labels naming both salts
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

Compound mass reference, 25 to 1,000 mg of elemental magnesium
Elemental magnesium	hydroxide compound	hydroxide size 00	sulfate compound	sulfate size 00
25 mg	60 mg	1	124–254 mg	1
50 mg	120 mg	1	248–507 mg	1
75 mg	180 mg	1	371–761 mg	1–2
100 mg	240 mg	1	495–1,014 mg	1–2
125 mg	300 mg	1	619–1,268 mg	1–2
150 mg	360 mg	1	743–1,521 mg	2–3
175 mg	420 mg	1	867–1,775 mg	2–3
200 mg	480 mg	1	991–2,028 mg	2–3

32 additional rows

Compound mass reference, 25 to 1,000 mg of elemental magnesium, additional rows
Elemental magnesium	hydroxide compound	hydroxide size 00	sulfate compound	sulfate size 00
225 mg	540 mg	1	1,114–2,282 mg	2–4
250 mg	600 mg	1	1,238–2,535 mg	2–4
275 mg	660 mg	1	1,362–2,789 mg	2–4
300 mg	720 mg	1	1,486–3,043 mg	3–5
325 mg	780 mg	2	1,610–3,296 mg	3–5
350 mg	840 mg	2	1,734–3,550 mg	3–5
375 mg	900 mg	2	1,857–3,803 mg	3–6
400 mg	960 mg	2	1,981–4,057 mg	3–6
425 mg	1,020 mg	2	2,105–4,310 mg	3–6
450 mg	1,080 mg	2	2,229–4,564 mg	4–7
475 mg	1,140 mg	2	2,353–4,817 mg	4–7
500 mg	1,200 mg	2	2,476–5,071 mg	4–7
525 mg	1,260 mg	2	2,600–5,325 mg	4–8
550 mg	1,320 mg	2	2,724–5,578 mg	4–8
575 mg	1,380 mg	2	2,848–5,832 mg	4–8
600 mg	1,440 mg	2	2,972–6,085 mg	5–9
625 mg	1,500 mg	3	3,096–6,339 mg	5–9
650 mg	1,560 mg	3	3,219–6,592 mg	5–10
675 mg	1,619 mg	3	3,343–6,846 mg	5–10
700 mg	1,679 mg	3	3,467–7,099 mg	5–10
725 mg	1,739 mg	3	3,591–7,353 mg	5–11
750 mg	1,799 mg	3	3,715–7,606 mg	6–11
775 mg	1,859 mg	3	3,839–7,860 mg	6–11
800 mg	1,919 mg	3	3,962–8,114 mg	6–12
825 mg	1,979 mg	3	4,086–8,367 mg	6–12
850 mg	2,039 mg	3	4,210–8,621 mg	6–12
875 mg	2,099 mg	3	4,334–8,874 mg	6–13
900 mg	2,159 mg	3	4,458–9,128 mg	7–13
925 mg	2,219 mg	4	4,581–9,381 mg	7–13
950 mg	2,279 mg	4	4,705–9,635 mg	7–14
975 mg	2,339 mg	4	4,829–9,888 mg	7–14
1,000 mg	2,399 mg	4	4,953–10,142 mg	7–14

Source · Chemical formulas and NIH DSLD labels · snapshot 2026-08-10 · release 2026-08-10-f441aa9f · CSV · method