A magnesium supplement can show several numbers that look comparable but describe different things. The front of a package might emphasize the weight of magnesium glycinate, citrate, or another compound. The Supplement Facts panel should separately declare the amount of magnesium itself. For product-to-product comparison, those figures cannot be treated as interchangeable.

The short version

Elemental magnesium is the mass of magnesium contributed by the ingredient. Compound weight includes magnesium plus the other parts of the chemical compound. A larger compound number does not automatically mean more magnesium.

The NIH Office of Dietary Supplements states that a Supplement Facts panel declares elemental magnesium rather than the full weight of a magnesium-containing compound. That is why LabelLens uses the declared magnesium amount as its primary active-amount field.

How to find the comparable number

1. Start with the Supplement Facts panel, not the marketing headline.
2. Confirm the serving size at the top of the panel.
3. Find the row named “Magnesium.” The milligrams on that row are the declared amount per labeled serving.
4. Read the parenthetical source—such as “as magnesium citrate”—as form context, not as a second active amount.
5. If a separate compound weight appears elsewhere, record it separately and never add it to the magnesium row.

A worked label-reading example

Imagine a label with a serving size of two capsules. The panel declares “Magnesium 200 mg (as magnesium bisglycinate)” while another part of the package refers to 1,400 mg of a bisglycinate material. The defensible comparison value is 200 mg of magnesium per two-capsule serving. Dividing by the serving size gives 100 mg per capsule. The 1,400 mg figure describes a different quantity and should stay in a compound-weight field if the source clearly supports it.

This separation prevents a product that advertises a heavy compound from appearing to provide several times more magnesium than it actually declares.

Why the serving size matters

FDA labeling guidance says a Supplement Facts panel includes the serving size and the quantity of each dietary ingredient per serving. A 200 mg declaration for one tablet is therefore not operationally identical to 200 mg for four capsules. LabelLens keeps the active amount and the required units together so readers can compare both concentration and pill burden.

What LabelLens will not infer

• We do not calculate elemental magnesium from compound weight using a theoretical percentage when the label does not declare the active amount.
• We do not assume every raw material with a similar chemical name has the same composition.
• We do not turn a front-label marketing number into a Supplement Facts value.
• We do not treat the declared amount as proof of absorption, suitability, or a personal dose.

A practical comparison checklist

Compare the same level of measurement: milligrams of declared magnesium per labeled serving, milligrams per capsule or tablet, and cost per labeled serving. Then inspect form, other ingredients, testing information, and source quality as separate attributes. If the label is unclear, the correct response is to withhold the calculation—not to manufacture precision.

Sources and further reading

• NIH Office of Dietary Supplements: Magnesium — Health Professional Fact Sheet
• FDA: Dietary Supplement Labeling Guide, nutrition labeling
• Electronic Code of Federal Regulations: 21 CFR 101.36

Source links were checked on July 18, 2026.