Two suppliers list the same compound. One asks $95 for a vial, the other $160. The first looks cheaper and frequently is not. Vial price is a number about a container; price per milligram is a number about material, and only the second one can be compared across a catalogue.
This guide covers the arithmetic, the three facts that quietly distort it, and the specific cases where a larger vial costs more per milligram rather than less. Everything here is procurement practice. It is not dosing or usage instruction, and the material discussed is supplied for laboratory research only.
The arithmetic, and why it is not quite enough
Price per milligram is vial price divided by the labelled mass. A 10 mg vial at $95.20 is $9.52 per milligram. A 60 mg vial at $361.20 is $6.02. On that basis the larger vial is 37 per cent cheaper per milligram, which is the kind of gap that decides a purchase order.
The figure is only as good as the mass you divide by, and the mass on a label is a nominal figure. What the certificate reports is the quantity that was actually measured. Where those two numbers differ, your real cost per milligram differs with them, and it differs in the supplier's favour rather than yours. Net peptide content is the line that resolves this, and it is the single most useful number on a certificate for anyone comparing prices.
Distortion one: net peptide content
A vial labelled 10 mg contains 10 mg of lyophilised solid. That solid is not pure peptide. It contains the peptide, the counter-ion it was isolated with, residual water, and whatever excipient was used as bulking agent. Net peptide content is the fraction that is actually the molecule you are buying, and on a research-grade certificate it is typically reported somewhere between 70 and 90 per cent.
The effect on price is direct. A 10 mg vial at $95.20 with a net peptide content of 80 per cent contains 8 mg of peptide, so the true figure is $11.90 per milligram rather than $9.52. A competing vial at $110 with a net content of 95 per cent contains 9.5 mg, which is $11.58. The vial that looked 15 per cent more expensive is in fact slightly cheaper. This reversal is common and it is invisible to anyone comparing shelf prices.
Two practical consequences follow. A supplier that does not report net peptide content cannot be price-compared at all, only guessed at. And a supplier that reports it is handing you the information needed to find them expensive, which is a reasonable proxy for how they treat buyers generally. Comparing suppliers on documentation rather than price takes that argument further.
Distortion two: the salt form
Most synthetic peptides are isolated as a salt, and the counter-ion travels with the molecule into the vial and onto the scale. Trifluoroacetate is the usual residue from preparative chromatography; acetate is the usual alternative where the material has been exchanged. The two forms differ in mass, so two vials with identical labelled masses and identical net peptide contents can still hold different quantities of peptide.
The difference is not enormous but it is not nothing, and it runs in the same direction as every other distortion: in favour of whoever is selling. TFA and acetate salt forms sets out the mass arithmetic. For price comparison the rule is simple — compare salt form to salt form, or compare net peptide content directly and let it absorb the difference.
Distortion three: the fill is not always what the name says
Blends complicate the calculation because the labelled mass is a sum. A vial listed as 5 mg / 5 mg holds two compounds and the price covers both, so a per-milligram figure means something different from the same figure on a single-compound vial. Comparing a blend against a single vial on price per milligram is comparing two unlike things, and the number will quietly favour the blend because it is dividing by a larger total.
The honest comparison for a blend is against the cost of the component vials bought separately. Blends and single vials covers what a combination product costs in documentation, which is the other half of that decision.
When the larger vial is not cheaper
The assumption that bigger is cheaper per milligram holds most of the time and fails often enough to be worth checking every time. Across the Restate catalogue there are listings where the largest available strength carries a higher per-milligram figure than the one below it.
| Strength | Vial price | Per milligram | Cheaper than the step below? |
|---|---|---|---|
| 10 mg | $95.20 | $9.52 | — |
| 20 mg | $159.60 | $7.98 | Yes |
| 30 mg | $215.60 | $7.19 | Yes |
| 48 mg | $397.60 | $8.28 | No |
| 60 mg | $361.20 | $6.02 | Yes |
How the same arithmetic reads across strengths of one listing
The 48 mg row is the instructive one. It is a larger vial than the 30 mg and it costs more per milligram, because a strength that exists to match a particular fill or a particular export requirement is priced against that purpose rather than against the ladder. A buyer working from the assumption that the biggest vial wins would pay $8.28 where $6.02 was available in a larger vial at a lower total price.
Checking this takes a minute per listing. The catalogue carries a per-milligram figure on the product card and on the product page precisely so the comparison does not depend on anyone doing the division by hand.
A worked basket
The method is easiest to see on a real comparison. Suppose two suppliers each list a 10 mg vial of the same compound. Supplier A asks $95.20 and publishes a certificate reporting 78 per cent net peptide content as the trifluoroacetate salt. Supplier B asks $118.00 and publishes 94 per cent as the acetate.
On shelf price, A is 19 per cent cheaper. On labelled mass, A is $9.52 per milligram and B is $11.80. On peptide actually present, A delivers 7.8 mg for $95.20, which is $12.21 per milligram, and B delivers 9.4 mg for $118.00, which is $12.55. The gap has closed from 19 per cent to under 3 per cent, and what remains is small enough that documentation quality, lead time and whether the supplier will still answer the phone in a year should decide it.
Run that comparison across a basket of ten lines rather than one and the aggregate frequently reverses. This is the single most useful hour of work available to anyone placing regular orders, and it needs nothing but a spreadsheet and published certificates.
Using the figure in a negotiation
Quoting price per milligram back to a supplier changes the conversation, because it demonstrates that the shelf price is not the number being evaluated. Three things follow from that.
A supplier who publishes net peptide content has already accepted the comparison and will generally engage with it. A supplier who does not publish it has to either produce the figure or explain why not, and the explanation is informative either way. And a request framed as cost per milligram of peptide rather than discount off list is harder to answer with a token percentage, because it points at a specific number rather than at goodwill.
The figure also travels upward inside your own organisation better than a vial price does. A budget line expressed as cost per milligram of material consumed is comparable year on year and across suppliers, where a list of vial prices is not.
What price per milligram does not tell you
It is a materials figure and nothing else. It says nothing about whether the lot has a certificate, whether that certificate names an accredited laboratory, whether purity was measured by a stated method, or whether the supplier will still exist when a question arises about a lot number eighteen months from now.
Those are the things that make a cheap vial expensive. A lot without a certificate cannot be used in work that needs to be defensible, which means its real cost is the cost of replacing it. What a certificate of analysis does not test for and the supplier audit checklist cover the part of value that no price figure reaches.
There is also a storage cost that price per milligram ignores entirely. A large vial is only cheaper if the whole vial gets used before it degrades. Buying 60 mg at $6.02 per milligram and using 20 mg of it costs $18.06 per milligram of material actually consumed, which is worse than buying the 20 mg vial outright. Peptide shelf life and freeze-thaw cycles and aliquoting govern how much of a large vial survives to be used.
A working method
Five steps, in order. First, divide vial price by labelled mass to get the shelf figure. Second, find net peptide content on the certificate and divide again by that fraction to get the true figure. Third, confirm the salt form matches whatever you are comparing against. Fourth, check the step above and below in the same listing rather than assuming the largest is cheapest. Fifth, ask whether the whole vial will be used inside its re-test window, and if not, run the arithmetic against the quantity you will actually consume.
Anything that survives those five steps is a real price. Anything that does not is a number about a container.
For purchase orders above a few vials the figure to negotiate against is this one, not the shelf price. How to read a wholesale peptide quote covers what else belongs on the quote, and volume pricing and bulk orders covers what changes when quantities rise.