Magnesium supplement labels can be confusing. Two products might both say "500 mg magnesium" on the front, yet deliver very different amounts of actual magnesium to your body. Understanding how to read the supplement facts panel — and what the key terms mean — will help you compare products accurately and avoid common pitfalls.
The Most Important Number: Elemental Magnesium
The single most important figure on a magnesium supplement label is the elemental magnesium content per serving. This is the actual amount of magnesium the supplement delivers, expressed in milligrams.
Magnesium supplements are compounds — magnesium bound to another molecule such as glycine, citric acid, or malic acid. The total weight of the compound is always higher than the weight of the magnesium it contains. For example:
- 500 mg of magnesium glycinate may provide approximately 50–60 mg of elemental magnesium
- 500 mg of magnesium citrate may provide approximately 75–80 mg of elemental magnesium
- 500 mg of magnesium oxide provides approximately 300 mg of elemental magnesium (but with much lower bioavailability)
Always look for the elemental magnesium figure in the supplement facts panel — it is usually listed in parentheses next to the compound name. This is the number to use when comparing doses across different products.
Identify the Form of Magnesium
The supplement facts panel will list the specific form of magnesium used. Common forms you will see include:
- Magnesium bisglycinate or glycinate — Chelated with glycine; high bioavailability, gentle on the stomach
- Magnesium citrate — Bound to citric acid; well-absorbed, mild laxative effect at higher doses
- Magnesium malate — Bound to malic acid; used for muscle and energy applications
- Magnesium L-threonate — Patented form; used for cognitive applications
- Magnesium oxide — High elemental content but low bioavailability; primarily used as a laxative
For a full comparison of magnesium forms, see How to Compare Magnesium Supplements. If you are deciding between the two most popular forms, see our detailed breakdown: compare magnesium glycinate and magnesium citrate.
Check the Serving Size
Serving sizes vary widely between magnesium products — from one capsule to four capsules per serving. Always check the serving size before comparing the elemental magnesium content between two products. A product listing 400 mg of elemental magnesium per serving may require four capsules to achieve that dose, while another delivers the same amount in two capsules.
Review the Other Ingredients
The "other ingredients" section lists excipients, fillers, capsule materials, and any additional compounds in the formula. Key things to look for:
- Capsule type — Gelatin (animal-derived) vs. vegetarian/vegan capsule (HPMC or pullulan)
- Allergen information — Check for gluten, soy, dairy, or other allergens if relevant to you
- Fillers and flow agents — Common excipients like magnesium stearate, silicon dioxide, and rice flour are generally considered safe; some people prefer to minimize them
- Added ingredients — Some magnesium formulas include cofactors like Vitamin B6, Vitamin D, or zinc; check whether these additions are relevant to your needs
Look for a Potency Guarantee
Quality supplement manufacturers guarantee the potency of their products through the expiration date, not just at the time of manufacture. Look for language on the label such as "potency guaranteed through expiration date" as an indicator of quality manufacturing standards.
Understand the % Daily Value
The supplement facts panel will show a % Daily Value (%DV) for magnesium based on a reference daily intake of 420 mg for adults. This figure gives you a quick sense of how the supplement's dose relates to general daily intake recommendations, but individual needs vary and the %DV is a general reference point rather than a personalized target.
Explore Magnesium Supplements
Browse our full selection of Magnesium supplements from established supplement brands including NOW Foods, Pure Encapsulations, Thorne, Bluebonnet Nutrition, and Douglas Laboratories. All products include clear supplement facts panels so you can compare elemental magnesium content and form with confidence.