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

Magnesium carbonate vs l-threonate: 694–807 vs 2,424 mg of compound for 200 mg of magnesium

Magnesium carbonate is 24.8–28.8% elemental magnesium and magnesium l-threonate is 8.3%, so 200 mg of magnesium needs 694–807 mg of carbonate against 2,424 mg of l-threonate: 1–2 vs 4 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 6 for l-threonate. Prices within each salt: no ranked carbonate price; l-threonate $1.1572 per 100 mg (a single ranked offer); observed 2026-10-26 to 2026-11-02.

computed from chemical formulas

carbonate for 200 mg Mg694–807 mg24.8–28.8% magnesium · 1–2 size 00

L-threonate for 200 mg Mg2,424 mg8.3% magnesium · 4 size 00

Exceeds size 000none · 0 of 6carbonate · l-threonate capsule labels

Cheapest by declared elemental magnesium, per 100 mg, within each saltcarbonate none · l-threonate $1.15720 and 1 ranked offers · 2026-11-02

Compound mass for the same elemental magnesium: dark dot carbonate (24.8–28.8%, lower mass bound), grey dot l-threonate (8.3%); the labels give each salt's full range.

Chart data

Chart labels and values for the main chart
Displayed chart text
100 mg magnesium
carbonate 347–404 · l-threonate 1,212
200 mg magnesium
carbonate 694–807 · l-threonate 2,424
400 mg magnesium
carbonate 1,387–1,614 · l-threonate 4,848

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 carbonate or l-threonate carries the same elemental magnesium?

At the same elemental amount, carbonate (24.8–28.8% magnesium) always needs less compound than l-threonate (8.3%): for 400 mg of magnesium, 1,387–1,614 mg against 4,848 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 carbonate and l-threonate
Elemental magnesium	carbonate compound	carbonate size 00	L-threonate compound	L-threonate size 00
100 mg	347–404 mg	1	1,212 mg	2
200 mg	694–807 mg	1–2	2,424 mg	4
400 mg	1,387–1,614 mg	2–3	4,848 mg	7

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 6 for l-threonate. 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 carbonate and l-threonate labels
Salt	Audited capsule labels	Fits 0 or 00	Needs 000	Exceeds 000
carbonate	0	0	0	0
L-threonate	6	6	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?

Compared only with offers of the same salt: no ranked carbonate price; l-threonate $1.1572 per 100 mg (a single ranked offer). 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

Price per 100 mg of declared elemental magnesium, within each salt
Salt	Ranked offers	Lowest per 100 mg	Median per 100 mg	Observed
carbonate	0	none	none	2026-11-02
L-threonate	1	$1.1572	$1.1572	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 l-threonate side by side?

No study in the PubMed-checked registry measured carbonate and l-threonate side by side as of 2026-08-10; 2 involve carbonate and 0 involve l-threonate separately.

measured

Registry studies involving carbonate or l-threonate
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

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

How many labels name both carbonate and l-threonate?

No label names both carbonate and l-threonate as of 2026-08-10, against 23 labels naming carbonate and 9 naming l-threonate.

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	carbonate compound	carbonate size 00	L-threonate compound	L-threonate size 00
25 mg	87–101 mg	1	303 mg	1
50 mg	173–202 mg	1	606 mg	1
75 mg	260–303 mg	1	909 mg	2
100 mg	347–404 mg	1	1,212 mg	2
125 mg	434–504 mg	1	1,515 mg	3
150 mg	520–605 mg	1	1,818 mg	3
175 mg	607–706 mg	1	2,121 mg	3
200 mg	694–807 mg	1–2	2,424 mg	4

32 additional rows

Compound mass reference, 25 to 1,000 mg of elemental magnesium, additional rows
Elemental magnesium	carbonate compound	carbonate size 00	L-threonate compound	L-threonate size 00
225 mg	780–908 mg	2	2,727 mg	4
250 mg	867–1,009 mg	2	3,030 mg	5
275 mg	954–1,110 mg	2	3,333 mg	5
300 mg	1,041–1,211 mg	2	3,636 mg	5
325 mg	1,127–1,312 mg	2	3,939 mg	6
350 mg	1,214–1,412 mg	2	4,242 mg	6
375 mg	1,301–1,513 mg	2–3	4,545 mg	7
400 mg	1,387–1,614 mg	2–3	4,848 mg	7
425 mg	1,474–1,715 mg	3	5,152 mg	8
450 mg	1,561–1,816 mg	3	5,455 mg	8
475 mg	1,648–1,917 mg	3	5,758 mg	8
500 mg	1,734–2,018 mg	3	6,061 mg	9
525 mg	1,821–2,119 mg	3	6,364 mg	9
550 mg	1,908–2,220 mg	3–4	6,667 mg	10
575 mg	1,994–2,320 mg	3–4	6,970 mg	10
600 mg	2,081–2,421 mg	3–4	7,273 mg	10
625 mg	2,168–2,522 mg	3–4	7,576 mg	11
650 mg	2,255–2,623 mg	4	7,879 mg	11
675 mg	2,341–2,724 mg	4	8,182 mg	12
700 mg	2,428–2,825 mg	4	8,485 mg	12
725 mg	2,515–2,926 mg	4–5	8,788 mg	13
750 mg	2,601–3,027 mg	4–5	9,091 mg	13
775 mg	2,688–3,128 mg	4–5	9,394 mg	13
800 mg	2,775–3,228 mg	4–5	9,697 mg	14
825 mg	2,862–3,329 mg	4–5	10,000 mg	14
850 mg	2,948–3,430 mg	5	10,303 mg	15
875 mg	3,035–3,531 mg	5	10,606 mg	15
900 mg	3,122–3,632 mg	5	10,909 mg	15
925 mg	3,208–3,733 mg	5–6	11,212 mg	16
950 mg	3,295–3,834 mg	5–6	11,515 mg	16
975 mg	3,382–3,935 mg	5–6	11,818 mg	17
1,000 mg	3,469–4,036 mg	5–6	12,121 mg	17

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