The Short Version
The biggest number on the front of a supplement bottle is the one most shoppers compare, and it is usually the wrong number. "400mg," "1500mg," "6000mg," "1200mg" most often describe the total weight of a compound, a low-potency raw powder, or a blend, not the amount of the active ingredient your body actually uses. We have scored hundreds of products across dozens of categories, and the same trap shows up again and again: the bestseller with the biggest front number frequently delivers one of the smallest real doses.
The fix is always the same. Ignore the front of the bottle, turn it over, and read the Supplement Facts panel for the number that matters: elemental magnesium, standardized curcuminoids, EPA plus DHA, grams of collagen, or per-strain CFU. Then compare products on cost per that real dose. This guide shows the trap in five common categories, with the actual math, so you can spot it anywhere. For the magnesium version in depth, see how much magnesium is actually in magnesium glycinate.
Why Brands Lead With the Big Number
It is simple psychology. On a crowded shelf or search page, "1500mg" looks stronger than "150mg," even when they describe the same product. The bigger figure is rarely false, it is just measuring the wrong thing: the weight of the whole compound or raw herb rather than the active fraction inside it. Because the front-of-bottle claim is marketing copy and the Supplement Facts panel is regulated, the honest number is almost always on the back, often in smaller type. Brands that lead with the active dose are the exception, not the rule.
The Trap, Category by Category
Magnesium: "400mg" can mean 60mg
Magnesium is bound to a carrier (glycine, oxide, citrate), and magnesium itself is only a fraction of that weight. Magnesium glycinate is about 14 percent elemental magnesium, so a "400mg" capsule typically delivers only about 56 to 60mg of usable magnesium. One popular 400mg bestseller lists exactly 60mg of elemental magnesium on its panel. The clinical target is 200 to 400mg of elemental magnesium, so a single "400mg" capsule is well short. See the magnesium glycinate scorecard.
Turmeric: "1500mg" can mean about 150mg of curcuminoids
What does the work in turmeric is the curcuminoids, concentrated in a standardized 95% extract. Many "1500mg turmeric" bestsellers are mostly cheap turmeric root powder (low in curcumin) with only a small amount of that 95% extract. One product with more than 100,000 reviews lists 1350mg of turmeric root plus just 150mg of 95% extract, so the actual curcuminoid content is around 150mg, not 1500mg. A dedicated extract product can deliver three to five times more curcuminoids from a smaller front number. See the turmeric and curcumin scorecard.
Fish oil: "1200mg" can mean 360mg of omega-3
The "1200mg" on a fish oil softgel is the total fish oil; the part that matters is the EPA plus DHA. Budget fish oils are often low-concentration, so a "1200mg" softgel may contain only about 360mg of omega-3, which means you need two or three softgels to reach a clinical EPA plus DHA dose. A concentrated product can pack 2000mg of EPA plus DHA into a single serving. Compare on EPA plus DHA, not total fish oil. See the fish oil scorecard.
Collagen: "6000mg" across six tablets is still a small dose
Collagen research generally uses 10 to 15 grams per day. A "6000mg" collagen product is 6 grams, below that range, and if it is a tablet you may be swallowing six pills to get even that. A standard peptide powder gives you 10 to 20 grams in one or two scoops. The front number sounds large in milligrams but is small in the grams that actually matter. See the collagen peptides scorecard.
Probiotics: the CFU you can see vs the strains you cannot
Probiotics flip the trap. The big "60 Billion CFU" is real, but it is a total across all strains, and many labels never tell you how much of each strain you are getting, or which strains have evidence for your goal. A high total CFU built from undisclosed or poorly studied strains is not better than a smaller, transparent, strain-specified product. Here the missing number is the per-strain count, not the headline. See the probiotic scorecard.
How to Find the Real Number in 15 Seconds
- Turn the bottle over and read the Supplement Facts panel. The front is marketing; the panel is regulated.
- Find the active line. Elemental "Magnesium" (with a %DV), "curcuminoids" or "95% extract," "EPA" and "DHA," grams of collagen, or per-strain CFU. That is your real dose.
- Check the serving size. The real number is per serving, and a serving may be two, three, four, or six pills, so divide accordingly.
- If only the compound or total is listed, do the quick math. Glycinate is about 14 percent elemental; turmeric root is low in curcuminoids; total fish oil is more than EPA plus DHA.
- If the active number is hidden, treat that as a yellow flag, not a selling point. Good products make the number that matters easy to find.
How We Score for This
Our rubric is built to defeat the label trap. We normalize every product to its real active dose and rank on cost per effective dose, not cost per pill or per front-label milligram. That is why our scores routinely place a clean, accurately dosed product above a louder bestseller with a bigger front number. Absorption matters too: even the right amount of an ingredient underperforms in a poorly absorbed form, which we cover in our guide to supplement bioavailability.
The Bottom Line
The number on the front of the bottle is chosen to sell; the number on the back is the one your body responds to. Across magnesium, turmeric, fish oil, collagen and probiotics, the pattern is the same: compare on the active dose, not the headline figure, and the genuinely good value usually looks different from the bestseller list. Flip the bottle over, find the real number, and divide by the serving size. For the deep dive on the clearest example, read how much magnesium is actually in magnesium glycinate.
These statements have not been evaluated by the FDA. This product is not intended to diagnose, treat, cure, or prevent any disease.