Pick up two magnesium bottles. One says 500 mg. One says 2,500 mg. The 2,500 mg bottle can easily contain less magnesium.
That is not a typo. It is the most expensive misunderstanding in the category, and one division on the back of the panel fixes it permanently. Learn it once and you will never overpay for a magnesium product again.
Why magnesium is worth getting right
Before the arithmetic, the reason to bother.
Magnesium is a cofactor in more than three hundred enzymatic reactions in the body. ATP — the currency every muscular contraction is paid in — is biologically active bound to magnesium; the working form is literally Mg-ATP. It contributes to normal muscle function, normal nervous-system function, normal protein synthesis, and normal energy-yielding metabolism.*
Those are not marketing lines. They are established physiological roles, which is a different tier of evidence from most of what gets sold at 22:00.
And there is a genuine gap to close. The recommended dietary allowance for adult men in the US sits at roughly 400 to 420 mg per day, and national intake surveys have consistently found a substantial share of adults consuming below the estimated requirement. Magnesium is abundant in leafy greens, nuts, seeds, legumes, and whole grains — and the average diet does not contain as much of those as the average person believes.
That is what makes the label arithmetic worth your ninety seconds. There is a real gap, and half the products sold to close it are printing a number that isn't magnesium.
Every magnesium label has two numbers
Compound weight is the total weight of the magnesium compound: the mineral plus whatever carrier molecule it is bound to. Magnesium glycinate, magnesium citrate, magnesium oxide.
Elemental magnesium is the weight of the magnesium itself, carrier stripped out.
Only the second number is magnesium. In most forms the carrier is heavier than the mineral it carries — sometimes far heavier.
Our own panel, Night Work, reads: 275 mg elemental magnesium from 2,500 mg magnesium glycinate. Both numbers, in that order, because one of them tells you what you are taking and the other one tells you what it weighs.
The chemistry, in one paragraph
Magnesium is a light atom. Bind it to a large organic carrier — glycine, citrate — and the carrier accounts for most of the finished molecule's weight. Bind it to something small and inorganic like oxygen and the mineral accounts for most of the weight instead.
Approximate elemental fractions
Calculated from molecular weights:
| Form | Roughly this much is magnesium |
|---|---|
| Magnesium oxide | ~60% |
| Magnesium citrate | ~16% |
| Magnesium bisglycinate | ~14% |
| Magnesium L-threonate | ~8% |
These are theoretical ceilings. Commercial raw materials come in lower, because real ingredients carry water of crystallisation, buffering agents, and processing carriers that pure molecular weight does not account for. Which is exactly why you want the elemental figure printed rather than calculated from a textbook.
And why you want it measured, which is a different thing again. The certificate of analysis for Night Work reports magnesium by ICP-MS at 96.91 mg per capsule, against a specification of more than 91.6 mg. Three capsules is 290.7 mg. Our label claims 275 mg. We claim less than the assay found — and both numbers are published, so you can check the subtraction rather than take the sentence. That is the whole argument of this article, run on our own panel: a printed elemental figure is better than a calculated one, and a measured figure is better than a printed one.
Why the biggest number is the one brands print
Look at which form has the highest elemental fraction. Magnesium oxide, at roughly 60%, lets a manufacturer put a large magnesium number on a small, cheap capsule.
It is also the form with the weakest absorption profile. Poor solubility means a substantial share passes straight through, and its most reliable effect at higher doses is a laxative one.
That is the trap. The form that produces the most impressive label is the form least likely to end up in you. A 500 mg oxide capsule and a 2,500 mg glycinate capsule can look similar on paper and behave nothing alike.
Chelated forms like glycinate carry the opposite trade: a lower elemental fraction, so the capsule has to be physically larger, in exchange for better tolerability. Glycine is a small, well-tolerated amino acid, and the resulting compound is markedly gentler on the gut than oxide at comparable elemental doses. You pay for that in capsule size. It is a trade worth making if you intend to take the thing every night for a year, which is the only way it does anything.
What 275 mg elemental is actually sized for
About 65% of the daily value, which is 420 mg on a supplement panel.
That number is deliberate, and the reason is a second published figure most brands never mention. There is a tolerable upper intake level of 350 mg per day for magnesium from supplements specifically. Food magnesium is not subject to it — the kidneys handle dietary magnesium comfortably — but supplemental magnesium is, and the ceiling is lower than a lot of bottles on the shelf.
275 mg sits under that ceiling. That headroom is the point — but it is 75 mg, not a licence, so here is our own arithmetic before anyone else's.
Training Water carries 60 mg of magnesium (as magnesium malate) per scoop. Run the full AM/PM protocol and your supplemental magnesium is 275 + 60 = 335 mg, which is under the 350 mg ceiling by 15 mg. That is deliberate and it is also the whole margin. If you add a multivitamin, a greens powder, or a second electrolyte product on top of both, you can cross the line — and loose stools will tell you before a label does.
We are printing that here rather than letting you find it, because a brand that teaches you to add up your stack has to add up its own first. Plenty of products carry magnesium quietly. Ours does not get to be one of them.
Where the evidence sits, honestly
Magnesium's established roles — normal muscle function, normal nervous-system function, normal energy metabolism — are the strongest thing about it and the honest basis for taking it.* They are also, conveniently, the roles that matter most to a man who trains: contraction, relaxation, nerve signalling, and the energy pathways underneath both.
The nervous-system role is why magnesium ended up as the internet's default evening supplement. We make no sleep claim for Night Work, and you will not find one anywhere on this site. The research on magnesium and sleep quality specifically is a smaller and less mature literature than the work establishing the physiological roles above, and we are not going to sell you the weaker half of the evidence just because it markets better. Night Work sits at 22:00 in the Protocol for two duller reasons: a fixed nightly slot is the easiest one in the day to keep, and the end of the day is when the systems magnesium contributes to are doing their work.*
Consistency is the mechanism. Timing folklore isn't.
The ceiling your gut will tell you about
Take too much supplemental magnesium, particularly in poorly absorbed forms, and the result is gastrointestinal and unmistakable. Loose stools are the standard signal and it is dose-dependent.
Treat that as useful feedback rather than a failure. If a magnesium product is running through you, the answer is less of it or a better-tolerated form, not more of it.
One practical note that matters: magnesium can interfere with the absorption of certain medications, including some antibiotics. If you take prescription medication of any kind, space your magnesium away from it and ask your doctor or pharmacist rather than guessing.
Reading any magnesium label in sixty seconds
- Find the elemental figure. If the panel gives only a compound weight with no elemental number, the brand is either careless or counting on you not to ask. Either is disqualifying.
- Divide. Elemental ÷ compound weight. Land near 60% and you are looking at oxide, whatever the front of the bottle says.
- Check the serving size. A "500 mg" claim spread across three capsules is a 167 mg capsule. Price the daily serving, not the headline.
- Read the form name exactly. "Magnesium glycinate" and "magnesium oxide blended with glycinate" are different products. Buffered blends are legitimate; they should be disclosed.
- Add up your whole stack. Multivitamins, electrolyte powders, and greens products all carry magnesium quietly. The 350 mg supplemental ceiling applies to your total, not to one bottle.
- Look for proprietary blends. If magnesium sits inside a blend with a single combined weight, you cannot calculate anything. Walk.
The bottom line
The number on the front of a magnesium bottle is compound weight. The number that decides what you are actually taking is elemental. They can differ by a factor of seven, and the direction of the difference is not the one most people assume.
Ours is 275 mg elemental from 2,500 mg of magnesium glycinate, 90 capsules — both numbers printed because both numbers are true. Roughly 65% of the daily value, under the supplemental upper limit, in the form built to be taken every night rather than to look impressive once.
Do the division. Then decide, on us or on anyone else. That is what The Monograph is for.
Also in the Journal: how to read a colostrum label, the same exercise on a different panel. Or run the full AM/PM system: the Recovery Standard.