Form · as filed on labels
Magnesium hydroxide
Magnesium hydroxide is 41.68% elemental magnesium by mass (Mg(OH)₂, molar mass 58.32). Every 100 mg of elemental magnesium from it needs 240 mg of the compound, calculated 2026-09-13. 6 on-market labels name this form. Median filed amount is 124 mg elemental magnesium per serving across 6 computed labels. 3 of these labels blend this form with other forms.
Chemistry · fixed
How much hydroxide carries how much magnesium
A US Supplement Facts panel declares the element, not the salt. Magnesium hydroxide has a molar mass of 58.32 against magnesium's 24.305, so 41.68% of its mass is magnesium.
| Elemental magnesium | hydroxide required | Size 00 capsules that much powder fills |
|---|---|---|
| 100 mg | 240 mg | 1 |
| 200 mg | 480 mg | 1 |
| 400 mg | 960 mg | 2 |
A size 00 capsule holds about 730 mg of powder at powder density 0.6–0.8 g/mL; a size 000 about 1,100 mg.
Mass budget across this form · computed
0 of 1 capsule labels naming this form exceed every standard capsule
| Fits a size 0 or 00 capsule | 1 |
|---|---|
| Requires the largest standard size, 000 | 0 |
| Exceeds every standard capsule | 0 |
Counted only for capsule labels naming this salt alone. Full method and the corpus-wide figure: label mass-budget audit.
Published measurements · peer-reviewed sources
1 published study has measured how this form is absorbed
Absorption is a separate question from mass, and a contested one. Below is what each study did, on whom, and what it measured — with the original linked. See the full literature page for why results conflict.
These entries report what each study measured and on whom. They are not advice, not a ranking, and not a claim about any product on this site. Every reference links to its PubMed record so the original can be read in full.
Comparing the Bioavailability of Two Seawater-Derived Magnesium Preparations.
- Design
- Double-blind, randomized, three-arm crossover study in 20 healthy young men and women: placebo (maltodextrin), seawater-derived magnesium citrate (Aquamin-Mg, minimum 10% elemental magnesium), and seawater-derived magnesium hydroxide (Aquamin-MgTg, minimum 33% elemental magnesium). Total magnesium doses were standardized to the RDA for elemental magnesium.
- What it measured
- Incremental 18-hour urinary magnesium excretion as the relative-bioavailability marker; serum magnesium concentration at 1 and 2 hours post-ingestion (colorimetric assay, run in triplicate).
- Limits
- Small sample (n=20); healthy young adults only, not a magnesium-deficient or older population; only two seawater-derived preparations plus placebo were tested, no head-to-head comparison against standard magnesium citrate/oxide/glycinate salts; short observation window (18 h urine, 2 h serum).
Median and range use the 6 labels with one determinable amount per serving, excluding any above 1,000 mg as filed. 0 of these labels carry an observed price in the gold set. This form has no priced EC100 table yet.
Labels filing this form 6
| Allergy Research Group | Magnesium Malate ForteNIH DSLD · Label 233224 · Tablet or Pill | citrate, hydroxide | 124 mg | 60 | 7.44 g | Not tracked yet |
| Allergy Research Group | Magnesium Malate ForteNIH DSLD · Label 304253 · Tablet or Pill | citrate, hydroxide | 124 mg | 60 | 7.44 g | Not tracked yet |
| Douglas Laboratories | Malic Acid + MagnesiumNIH DSLD · Label 232010 · Tablet or Pill | hydroxide | 86 mg | 180 | 15.48 g | Not tracked yet |
| Irwin Naturals | Magnesium + AshwagandhaNIH DSLD · Label 323288 · Softgel Capsule | hydroxide | 150 mg | 20 | 3.00 g | Not tracked yet |
| NutriCology | Magnesium Malate ForteNIH DSLD · Label 235240 · Capsule | citrate, hydroxide | 124 mg | 60 | 7.44 g | Not tracked yet |
| PureBulk.com | Magnesium HydroxideNIH DSLD · Label 23167 · Powder | hydroxide | 417 mg | 250 | 104.25 g | Not tracked yet |
See all forms, brands, or the priced form matrix.
Compare hydroxide with other salts
13 published comparisons include magnesium hydroxide as of 2026-09-13; each row gives the other salt's magnesium fraction and compound mass for 100 mg elemental magnesium from the chemistry model.
- Magnesium hydroxide vs magnesium citrate: 11.3–16.16% magnesium by mass; 619–885 mg compound per 100 mg elemental magnesium.
- Magnesium hydroxide vs magnesium glycinate: 11.83–14.1% magnesium by mass; 709–845 mg compound per 100 mg elemental magnesium.
- Magnesium hydroxide vs magnesium oxide: 60.32% magnesium by mass; 166 mg compound per 100 mg elemental magnesium.
- Magnesium hydroxide vs magnesium malate: 13.2–15.54% magnesium by mass; 644–758 mg compound per 100 mg elemental magnesium.
- Magnesium hydroxide vs magnesium aspartate: 8.42% magnesium by mass; 1,188 mg compound per 100 mg elemental magnesium.
- Magnesium hydroxide vs magnesium carbonate: 24.78–28.83% magnesium by mass; 347–404 mg compound per 100 mg elemental magnesium.
- Magnesium hydroxide vs magnesium gluconate: 5.86% magnesium by mass; 1,706 mg compound per 100 mg elemental magnesium.
- Magnesium hydroxide vs magnesium chloride: 11.96–25.53% magnesium by mass; 392–836 mg compound per 100 mg elemental magnesium.
- Magnesium hydroxide vs magnesium taurate: 8.85% magnesium by mass; 1,130 mg compound per 100 mg elemental magnesium.
- Magnesium hydroxide vs magnesium l-threonate: 8.25% magnesium by mass; 1,212 mg compound per 100 mg elemental magnesium.
- Magnesium hydroxide vs magnesium orotate: 7.27% magnesium by mass; 1,376 mg compound per 100 mg elemental magnesium.
- Magnesium hydroxide vs magnesium lactate: 12.01% magnesium by mass; 833 mg compound per 100 mg elemental magnesium.
- Magnesium hydroxide vs magnesium sulfate: 9.86–20.19% magnesium by mass; 495–1,014 mg compound per 100 mg elemental magnesium.
Excipients most common in hydroxide labels
5 published excipient facets below have the highest frequencies among 10 labels mentioning magnesium hydroxide in the NIH DSLD records, counted 2026-09-13; each label enters an ingredient count once.
- croscarmellose sodium: 4 of 10 labels.
- microcrystalline cellulose: 4 of 10 labels.
- stearic acid: 4 of 10 labels.
- gum acacia: 3 of 10 labels.
- magnesium stearate: 3 of 10 labels.
The metric
What EC100 measures
EC100 = container price ÷ (elemental mg per serving × servings per container ÷ 100)
It normalizes the declared elemental amount to a 100 mg unit. It does not score ingredients, quality, or outcomes.