The number on the front isn't the mineral
Minerals can't exist alone in a pill — they're bound to another molecule to form a stable compound (a salt or a chelate). That means a label saying 'Calcium carbonate 1,250 mg' does not provide 1,250 mg of calcium; the rest of the weight is the carbonate. The amount of the actual mineral is called the elemental content, and it's what your body can use [2].
Examples of the gap
The elemental percentage varies a lot by compound:
- Calcium carbonate is about 40% elemental calcium; calcium citrate is about 21%.
- Magnesium oxide is about 60% elemental magnesium but poorly absorbed; magnesium glycinate is a lower percentage but better tolerated (see [chelated minerals](/learn/chelated-minerals-explained)).
- Iron supplements list the salt (ferrous sulfate, gluconate, bisglycinate), each with a different elemental iron amount.
A good label states the elemental amount directly — for example, 'Magnesium (as magnesium glycinate) 200 mg' means 200 mg of elemental magnesium.
Why this matters for dosing and safety
Research doses and the Tolerable Upper Intake Levels are expressed as elemental amounts. If you compare a product's *total* compound weight to an elemental dose, you'll overestimate what you're getting — and a 'high-dose' label may deliver less actual mineral than a competitor. It also matters for safety: the upper limit for, say, zinc or iron refers to elemental milligrams [1].
How to read a mineral label
1. Find the line listing the mineral and its form, e.g., 'Zinc (as zinc picolinate).'
2. Use the number next to the mineral name — that's the elemental amount.
3. Compare products on elemental amount per serving, and check it against the recommended intake and upper limit.
4. Remember absorption differs by form too (see bioavailability explained) — elemental amount and absorption together determine what you actually use.