Price per mg: is one vial really cheaper than a kit?

How this tool works · sources read October 28, 2026 · Grey Peptides Editorial Board

What the calculator computes

The calculator puts two offers for the same compound on one footing. For each offer you enter the total price you pay, the number of vials and the labelled milligrams (mg) in each vial. It works out:

cost per vial = price ÷ vials
total content = vials × mg per vial
cost per mg = price ÷ total content

Cost per mg is the number to compare. A listing shows the price of a vial, and a vial of one strength is not comparable with a vial of another, or with a box of ten. Divided by milligrams, two offers of the same compound become two prices for the same thing.

If you enter a dose, in mg or micrograms (1 mg = 1,000 mcg), it adds the per-dose figures. Cost per dose by content is cost per mg × dose: what the milligrams in one dose cost. Whole doses per vial is the vial's content divided by the dose, rounded down, and cost per dose, whole doses only is the cost per vial divided by that number. The second figure is the one you actually pay, because the powder left in a vial after its last whole dose is paid for and not used. The calculator shows how much is left in each vial so you can see the waste. With doses per week it also gives the cost per week and how many weeks each offer lasts.

The comparison under the table gives the ratio of the two prices per mg, the difference per mg, per dose and per week, and what the larger offer's milligrams would cost at the other offer's price per mg. You never pick a peptide: the arithmetic is the same for every compound.

The worked example

The example button loads the case from our guide to kits versus single vials, labelled there as an example and not a quote (as of October 28, 2026): $400 for one 15 mg vial (Offer A) against $300 for a kit of ten 15 mg vials (Offer B). The calculator shows $400 and $30 per vial, $26.67 and $2.00 per mg, a ratio of 13.3, and $4,000 for the kit's 150 mg bought at Offer A's price per mg, $3,700 more than the kit. Those numbers are also the calculator's own test case: before the page is published, the arithmetic is run in node against hand-worked answers for this example and eight others, including microgram doses, a dose larger than the vial and offers of different strengths.

The 28-day option

An opened multiple-dose vial from a manufacturer is dated when first punctured and discarded within 28 days unless the manufacturer gives another date.¹ That is a sterility rule and an outer limit, not a measured time that a peptide you mix yourself stays intact: the bacteriostatic water label says a drug dissolved in it should be used promptly and not stored unless the drug's maker directs otherwise.² With the option on, which is the default and the rule our cost calculator also uses, a vial is never counted for more doses than 28 days of your schedule use, so a vial that holds many small weekly doses is costed by the doses you could use, not by its content. Turn it off to cost by content alone.

Why nothing is filled in

The fields start empty. Any price we filled in would be some seller's price, and this site names and links no sellers; a dose filled in would look like a recommendation. Enter the prices you are actually offered, with shipping and any testing fee included in the price, and your own dose. Where a compound has a sourced dose, its encyclopedia entry shows it in the Recommended dosing box with the label or trial it comes from.

What it leaves out

What is really in the vial. The calculator trusts the label. When researchers bought semaglutide from online sellers that required no prescription, the vials held 29% to 39% more than their labelled amount, and one vial measured 8.95 EU/mg of bacterial endotoxin.³ A mislabelled vial changes both the dose and the real price per mg.

A failed batch. A kit is usually ten vials from one batch, so a bad batch loses all of them. The calculator compares prices, not the chance that either offer is what its label says; our guide to kits covers that trade-off.

Supplies and storage. Water, syringes and the cost of keeping ten vials cold for months are not counted. A kit means months of storage; mix one vial at a time.

Mixing. The volume of water does not change the cost. To turn a dose into syringe units, use the reconstitution calculator.

Sources

1. The Joint Commission. Multi-dose vials: managing multi-dose vials of injectable medication (standards FAQ): an opened or accessed multiple-dose vial from a manufacturer is dated and discarded within 28 days unless the manufacturer specifies a different date. Read September 30, 2026. Joint Commission
2. Hospira, Inc. Bacteriostatic Water for Injection, USP, prescribing information: multiple-dose container; when diluting or dissolving drugs, mix thoroughly and use promptly, and do not store reconstituted solutions of drugs for injection unless otherwise directed by the manufacturer of the solute. DailyMed set 87d6e9dc, version 20; storage wording re-read October 27, 2026. DailyMed
3. Ashraf, A. R. et al. (2024). Multifactor Quality and Safety Analysis of Semaglutide Products Sold by Online Sellers Without a Prescription: Market Surveillance, Content Analysis, and Product Purchase Evaluation Study. Journal of Medical Internet Research, 26, e65440. PMID: 39509151 · doi:10.2196/65440

This explainer describes how the tool works and what its numbers rest on. It is not medical advice and does not recommend any dose or product.