Methodology & Sources

The formulas

Every tool on the site runs the same few calculations, in this order.

Concentration is the vial amount in mcg divided by the water volume in mL. Draw volume is your dose in mcg divided by the concentration. Units are the draw volume times 100, because one unit on a U-100 syringe is 0.01 mL. Doses per vial is the vial amount divided by the dose, rounded down to whole doses. The bit left over, if there is one, gets shown rather than quietly dropped.

Reverse mode solves for water instead. The water in mL equals the target units times the vial amount, divided by the dose times 100. That result is rounded to the nearest 0.1 mL, and then everything is recalculated from the rounded amount. So the units you see are the units that water amount really produces, not the tidier units the exact fraction promised.

Blend mode keeps a separate concentration for each compound in the vial: its own amount divided by the shared water. A draw sized for one compound is then multiplied by every other compound's concentration, which is how the result can tell you what else the draw carries.

Rounding only ever happens at the end, for display. Units to one decimal place, with the nearest half-unit mark noted. Volumes to two decimals. Concentrations to whole mcg per mL. Nothing gets rounded mid-calculation, because small roundings compound into visible errors.

How the numbers are produced, and checked

One piece of code, the engine, powers every calculator, table, chart and the downloadable PDF on this site. When the site is built, the tables are generated from it. Nobody types a calculated value into a page by hand. That rule sounds fussy until you hear why it exists: while this site was being built, a draft table written by hand had a water amount wrong in it, and the engine's tests caught it. Hand-typed numbers fail exactly that way, quietly, and nobody notices. So there are none.

The engine carries a suite of test cases with results known exactly. For example, a 5 mg vial with 2 mL of water and a 250 mcg dose has to produce 2,500 mcg/mL, a 0.10 mL draw, 10 units and 20 doses per vial, or the build fails. There are cases like that for standard mode, reverse mode and blends of two, three and four compounds. A second suite covers the edges: zero, blank and out-of-range inputs; a dose bigger than the whole vial; draws landing just under and just over the 30, 50 and 100 unit capacities of the three syringe sizes; and damaged or nonsense share links, which have to fall back to defaults instead of breaking the page. Any change to the formulas reruns everything before it can go live.

The vial sizes offered as presets are common catalogue sizes. Each one was checked against at least two supplier catalogues before it was added. Treat them as a typing shortcut and nothing more. The calculation always uses the amount you enter, and the amount you enter should be the amount on your own vial's label.

Where the facts come from

The arithmetic needs no source. It is arithmetic. The facts around it do, and here they are.

The 28 day dating for multi-dose vials comes from the United States Pharmacopeia (USP) and its beyond-use dating standards: 28 days after a multi-dose vial is first punctured, unless the manufacturer specifies a different period.

The details about bacteriostatic water come from manufacturer labelling for Bacteriostatic Water for Injection: 0.9% benzyl alcohol as the preservative, storage at 20 to 25 °C. Sterile water for injection is labelled preservative-free and single-dose, which is the whole practical difference between the two.

The reason this site is so insistent about units not being a dose is documented by the US Food and Drug Administration (FDA). Its safety communications on compounded GLP-1 products describe patients mis-measuring by large factors after confusing units, millilitres and milligrams, some of them ending up in hospital. That record is why every result here shows your dose in both mg and mcg, right next to the units.

Syringe numbers are labelling conventions. U-100 means 100 units per millilitre. U-40 means 40. Nothing more exotic than that, and worth knowing because the two are easy to mix up.

For the scale of the confusion itself, there is a published analysis of about 302,000 posts from the largest peptide discussion community on Reddit, which found roughly 11% of posts involve dose calculation confusion of one kind or another. We cite it for the size of the problem. Never as a source for any fact about a substance.

Regulatory status of the compounds

Correct as of 1 November 2026, taken from the regulators named. This section gets updated when regulators publish changes, and every update lands in the log below. It exists so that nobody mistakes a powder vial for an approved medicine.

Tirzepatide has FDA-approved medicines, sold as prefilled pens. Loose powder vials of tirzepatide are not FDA-approved medicines.

Semaglutide also has FDA-approved medicines, pens and tablets. Loose powder vials of semaglutide are not FDA-approved medicines either, and the FDA has published safety communications about compounded semaglutide, including the dosing errors mentioned above.

Retatrutide is investigational. It is in clinical trials and is not approved by the FDA, or by any other medicines regulator, for any use.

BPC-157 is not an FDA-approved medicine. In 2023 the FDA placed it in Category 2 of its list of bulk substances for pharmacy compounding, the category for substances it has flagged as raising significant safety concerns.

DoseUnits sells nothing and links to no sellers. The calculators do the same maths whatever the substance is. That neutrality is deliberate, and it is not an endorsement of anything.

Corrections and change log

Found a wrong number, or a source that has moved? Tell us through the contact page. Anything verified gets fixed, and the fix is recorded here with its date. Changes to facts anywhere on the site get logged the same way. A public log keeps us honest in a way a quiet edit never would.

1 Nov 2026. Site launched. Formulas and both test suites in place, preset vial sizes checked against two catalogues each, regulatory status section first published.