Reference

Glossary

19 terms used across the label, salt, ranking and audit pages, each with the rule the pages apply. The full method is on the methodology page.

Elemental magnesium: The magnesium itself, counted in milligrams on a US Supplement Facts panel. The rest of a salt's weight is the partner molecule (citrate, glycinate, oxide and so on).
Compound (salt) mass: The weight of the whole magnesium salt that has to be in a serving to deliver the declared elemental magnesium: elemental mg ÷ elemental fraction.
Elemental fraction: The share of a salt's mass that is magnesium, fixed by its molecular formula: magnesium oxide 60.3%, magnesium citrate 11.3–16.2%, magnesium glycinate 11.8–14.1%.
Hydrate range: When a salt can carry water of crystallisation and labels do not say which form, its elemental fraction is a range and every derived mass is a range too.
Most favourable reading: Every capsule verdict uses the highest possible elemental fraction and the largest number of units per serving, so a label only fails when it fails under every reading.
Capsule sizes 0, 00, 000: Standard hard capsules hold about 545 mg (size 0), 730 mg (00) and 1,100 mg (000) of powder at a powder density of 0.8 g/mL, the top of the usual 0.6–0.8 range, so every verdict favours the label.
Capsule fill verdict: Fits size 0, needs size 00, needs size 000, or exceeds every standard capsule, computed from the compound mass per capsule at the most favourable reading.
Price per 100 mg of elemental magnesium (EC100): Observed container price ÷ (declared elemental mg per serving × servings per container ÷ 100). Prices are compared only within one salt.
Ranked offer: A retail offer whose brand, salt, form, dose and pack size match the label (status confirmed or verified). Only ranked offers enter rankings, medians and percentiles; one offer counts once.
On review: An observed offer whose pack size or dose does not yet match the label (status likely or provisional). It is shown with its date but enters no ranking.
Verified and confirmed prices: Verified: a price row matched to the label by hand in August 2026 that also passes every automatic check. Confirmed: brand, salt and dose or unit count match the label in the September 2026 check, and every automatic check passes. Only these two enter a ranking, a median or a percentile; likely and provisional rows are shown as on review.
Percentile and band: A label's price position among ranked offers of the same salt, given on a label's page from 5 offers. On a salt page the band between the 25th and 75th percentiles is shown from 3 offers and marked unstable with 3–4.
Percent Daily Value: Declared elemental magnesium ÷ the reference amount for a group (420 mg for adults and children 4 and older, 21 CFR 101.9) × 100. A difference from the label can reflect an older reference.
NIH DSLD: The Dietary Supplement Label Database of the NIH Office of Dietary Supplements: the filed label text this site recomputes. Use does not imply endorsement by NIH.
FDA CAERS: The FDA adverse event reporting system for foods and supplements. openFDA states that reports “cannot be used to estimate the incidence of these events”; this site shows them at brand level only.
Filed formulation cluster: Labels from different brands with the same filed ingredient list, shell, units per serving and elemental amount per unit (rounded to 5 mg). Labels do not name who makes the product.
Class of compounds: A name such as "amino acid chelate" that covers many substances; it has no single formula, so no elemental fraction or compound mass can be computed.
Data release: The version of the numbers on a page: registry snapshot date plus a fingerprint of the price file. Charts and CSV files carry the release in their names and never change.
Claim identifier: Every computed sentence carries an identifier, so a correction request can point to the exact claim.