ElementalDose: label arithmetic for US magnesium supplement labels (NIH DSLD snapshot 2026-08-10)

Arithmetic on each label's own declaration, always at the reading most favourable to the product: not a laboratory assay, not a finding that any product is mislabeled, and not medical or intake advice. A US Supplement Facts panel declares elemental magnesium per serving, not the mass of the magnesium salt needed to deliver it. This dataset recomputes, for all 716 on-market magnesium labels in the NIH Dietary Supplement Label Database snapshot of 2026-08-10, the compound (salt) mass per serving and per capsule from each salt's molecular formula, and compares it with standard capsule capacities (size 0 about 545 mg, 00 about 730 mg, 000 about 1,100 mg at powder density 0.8 g/mL, the top of the usual 0.6–0.8 g/mL range). Of 197 capsule labels that name a single salt, 36 declare more magnesium than the named salt alone could deliver from a size 000 capsule, and 66 need the largest standard size. The deposit contains the per-label table (716 rows), the audit subset (102 rows), a registry of 16 peer-reviewed studies that measured magnesium salts (bibliographic metadata and PubMed identifiers in the studies file), and a README with the method and a column dictionary. Retail prices shown on the website are not included. Live pages, charts and per-page CSV files: elementaldose.com/data. Version 2026-09-26: capsule verdicts use the larger of the serving field and the container count ÷ servings (6 labels moved from exceeds-all to needs-000); 3 labels filed as malate but described as dimagnesium malate are no longer treated as magnesium malate (36 of 197 now exceed every standard capsule, against 43 of 200 in version 2026-09-25); the capacity caption states the density at which capacities hold.