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Magnesium supplements: how to read the numbers

The big number on the front of a pack is usually not the magnesium you get. Here’s where to find the figure that is, and how to read our list.

Why 500 mg on the front isn’t 500 mg of magnesium

The front shows the whole compound. The magnesium you actually get is a smaller figure on the back.

Magnesium is always bound to a partner, such as oxide, citrate or glycine. The big front number is usually that whole compound. The magnesium comes after “equivalent to” or “from” in the panel.

How much is magnesium depends on the partner. 500 mg of oxide gives about 300 mg of magnesium. 500 mg of glycinate gives about 70 mg, and aspartate about 37 mg.

Why it matters to you: two packs that both say “500 mg” can hold very different amounts of magnesium. Price per tablet won’t show it. Cost per 100 mg of magnesium will.

Labels call this elemental magnesium, and every mg figure in our list means that. To check a pack, try the calculator.

Reading the list, column by column

Compare “Cost per 100 mg” within one form. The other columns tell you how far to trust it.

Form
The compound the source names. Compare within one form to compare like with like.
Label says
Magnesium per serve, from the pack, the brand’s page or a shop listing. It’s the figure you’re given, so our costs use it.
Our maths
The compound weight × its share of magnesium. If it matches “Label says”, the label’s figures agree.
Adds up?
Whether the two are within 15 %, or why we can’t tell. See the marks below.
Testing
Whether we could open a test certificate. A claim on the pack isn’t enough.
Cost per 100 mg of magnesium
Price ÷ serves ÷ magnesium per serve × 100. It puts a 37 mg tablet and a 300 mg tablet on the same scale. The median across our list is $0.25.
Cost per serve
Price ÷ serves. Handy for budgets, but not a fair comparison: serves hold different amounts.
Price used
The recommended retail price (RRP), or the regular shelf price if there’s no RRP, with pack, shop and date. A sale may be cheaper. No RRP yet means no cost. Prices older than 35 days say “may have changed”.

What the marks mean

Each mark says what we checked and what we found. None of them is a lab test.

Does the label add up?

adds up
The compound weight carries the stated magnesium, within 15 %. The cost per 100 mg rests on figures that agree.
mostly adds up
For blends, we check each compound on its own. One part often can’t be checked, usually an unnamed “amino acid chelate”. If every other part adds up, and they make at least 50 % of the magnesium, it mostly adds up. The % shows how much we checked.
stated mg above maths
stated mg below maths
The stated magnesium is over 15 % above or below what the stated compound carries. We use these only for the pack, the brand’s page or the ARTG, after emailing the brand and waiting seven days. Ordinary reasons include a second compound, rounding or a typo. Ask the brand which figure the product is made and tested to.
listing figures don’t match
A shop listing’s two figures don’t agree, and we haven’t seen the pack yet. Listings are typed by hand, so this says nothing about the product. The back of the pack settles it.
under review
We’re checking a source that may change the mark, or waiting for the brand to reply.
can’t check: compound unclear
No single share of magnesium, such as “amino acid chelate” with no amino acid named.
can’t check: no compound weight
Only the magnesium figure is given, so there’s nothing to check it against.
magnesium mg not given
Only the compound weight is given. We worked out the magnesium.
no figures yet: no ingredient panel found
The page we used had no ingredient panel, so we removed its figures until we read the pack.

Why “can’t check” matters to you: it’s common, and it isn’t a mark against the product. Cost per 100 mg still works, because it uses the magnesium figure the source gives.

Testing

test document linked
We opened a test certificate. It shows testing happened, not that your batch was tested.
testing claimed, no document found
Described as tested, but we found no certificate. That doesn’t mean testing didn’t happen.
no testing claim found
True of most products here, and not a mark against them.

Why it matters to you: if testing matters, ask the brand for the certificate. An AUST L number doesn’t mean the TGA checked the product before sale; the FAQ explains.

Compare like with like

Each form has its own page, so the costs sit side by side on equal terms.

For the chemistry, see which magnesium is which.

What the list can’t tell you

  • Whether you need magnesium, which form or how much. Ask a pharmacist or doctor.
  • What’s inside a tablet. We don’t test.
  • The whole market. We list 15 products so far. If yours is missing, nothing follows from that.

All products listed

Page text last revised 27 Oct 2026.