Tool
Cost per verified milligram
The number a price tag cannot give you. Enter what you paid, what the label claimed, and what a laboratory measured.
Sticker price per mg
$9.00
Price ÷ labelled mass, assuming the label.
Cost per verified mg
$9.18
Price ÷ (labelled mass × measured purity). What a milligram of the actual compound costs.
Difference
+2%
0.2 mg of the labelled mass is not the compound.
Enter a measured purity from a result you trust. VialPost does not supply a default purity figure, because assuming one would defeat the point of measuring it.
The arithmetic
Why the sticker price flatters the vial
Price per milligram is the standard way this market is compared, and it quietly assumes something nobody has checked: that a milligram of product is a milligram of compound. Purity is the term that converts one into the other, and it is the term vendors are least often held to.
The effect is not symmetric with intuition. Purity sits in the denominator, so the cost penalty grows faster than the shortfall: a vial measuring 80% against a 99% claim does not cost 19% more per real milligram, it costs roughly 24% more. That is why the delta is worth measuring rather than estimating.
Compare observed prices per milligram · see measured purity in the registry
Questions
About this calculator
- What is cost per verified milligram?
- The vial price divided by the mass that a laboratory measured as actually being the compound: price ÷ (labelled mass × measured purity ÷ 100). Sticker price per milligram divides by the labelled mass alone, which assumes the label is correct.
- Why does a few percent of purity matter?
- Because it compounds with price. A vial at 90% measured purity delivers ten percent less compound than its label implies, so the real cost per milligram is about eleven percent higher than the sticker figure. Between two listings a few percent apart on price, purity can invert which one is cheaper.
- What purity figure should I enter?
- One from a result you trust — ideally a third-party assay against a reference standard, with a lot number that matches the vial in front of you. VialPost deliberately supplies no default purity value, because assuming one would defeat the purpose of measuring it.
- Can I trust a certificate of analysis supplied by the seller?
- Treat it as a claim rather than a measurement. A vendor-supplied certificate that carries no lot number matching your vial, no date, no named laboratory, or no reference standard cannot be checked, and a certificate that can be produced by the party being assessed is not an independent result.
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