What this calculator does — and does not do
Retatrutide is an investigational peptide with no approved dose anywhere; in clinical trials it is supplied in pre-filled pens, so nobody in a trial ever reconstitutes anything. The arithmetic questions people search for — how much diluent, how many units — arise only with lyophilised powder, which is how unlicensed material is sold. This page explains and computes that arithmetic because concentration math is the same for every peptide and getting it wrong is the most common source of ten-fold errors. It does not suggest an amount, a schedule or a route. The trial regimens, with the weight and HbA1c results each produced, are listed on the dosing guide.
The three numbers
Every reconstitution problem has three quantities and one relationship. The vial contains a stated mass of peptide (milligrams). A volume of diluent (millilitres) is added. Concentration is mass divided by volume. Once the concentration is known, any amount of peptide corresponds to a volume: amount divided by concentration. On a U-100 insulin syringe, 100 units equals 1 mL, so volume in units is volume in millilitres multiplied by 100. That is the whole calculation, and the tool below performs it for whatever numbers are entered.
| Vial | Diluent added | Concentration | An amount of 1 mg corresponds to | On a U-100 syringe |
|---|---|---|---|---|
| 10 mg | 1 mL | 10 mg/mL | 0.10 mL | 10 units |
| 10 mg | 2 mL | 5 mg/mL | 0.20 mL | 20 units |
| 10 mg | 3 mL | 3.33 mg/mL | 0.30 mL | 30 units |
| 5 mg | 1 mL | 5 mg/mL | 0.20 mL | 20 units |
| 5 mg | 2 mL | 2.5 mg/mL | 0.40 mL | 40 units |
Milligrams, micrograms and units are different things
The three classic mistakes all come from unit confusion. A milligram is 1,000 micrograms; a vial labelled 10 mg contains 10,000 mcg, and a calculation done in the wrong unit is off by a factor of a thousand. A syringe “unit” is a volume, not a mass — 1 unit is 0.01 mL — so the number of units that corresponds to a given amount depends entirely on the concentration chosen at reconstitution, and a chart that gives units without stating the concentration is meaningless. Finally, adding more diluent does not change the amount of peptide in the vial; it only spreads the same mass over a larger volume, which makes small amounts easier to measure and large amounts require bigger draws.
Why diluent volume is a choice, not a rule
There is no correct amount of bacteriostatic water for a 10 mg vial. More diluent gives a lower concentration and a larger, easier-to-read volume for any given amount; less diluent gives a higher concentration and a smaller draw. Laboratory practice usually picks a volume that puts the expected working amounts in the 0.1–0.5 mL range, avoids the imprecision of drawing under 5 units, and stays within the vial's headspace. The bacteriostatic-water guide covers the diluent itself — what it is, why 0.9% benzyl alcohol, and how long a reconstituted solution is expected to remain usable under refrigeration.
How trial doses relate to this
The retatrutide trials used once-weekly subcutaneous doses of 1, 4, 8, 9 and 12 mg (plus 0.5 mg in the phase 2 diabetes study), reached by stepwise escalation from a 2 mg or 4 mg starting dose. Those milligram figures are masses of peptide delivered from a pre-filled pen; they say nothing about concentration or volume, and they were chosen for a supervised protocol in a screened population with a defined escalation schedule. Reading them alongside the calculator does not turn either into a recommendation. The dosing guide presents every published arm with its results, and the side-effects guide explains why the escalation schedule mattered.
The legal and quality context
Retatrutide is not approved in any jurisdiction as of September 2026. Marketing it for human use is illegal in the US, Canada and the EU, and vials sold as retatrutide have repeatedly failed independent testing for content, purity and sterility — which means the “10 mg” on the label, the first number in every calculation on this page, is itself unverified. This tool exists because concentration arithmetic is part of peptide science education, and because a wrong calculation is dangerous regardless of the substance. It is not guidance on obtaining or using any product.
Reconstitution calculator
Enter how much peptide is in the vial and how much diluent (e.g. bacteriostatic water) is added. The tool returns the resulting solution concentration — and, for any amount you type, the volume it corresponds to. This is educational arithmetic, not a dosing recommendation.
Enter an amount to see the volume it corresponds to.
Educational concentration mathematics only. This tool does not recommend a dose, amount, or protocol, and nothing here is medical advice. Many peptides are not authorized by Health Canada for human use — see our reconstitution and bacteriostatic-water guides for context.
Sources and what they cover
These primary studies, official records and standards cover the topics linked below. The scope notes distinguish laboratory findings, human trials and regulatory records. This is a selected bibliography, not a systematic review or verification of every sentence; absence of a study here does not prove that no study exists.
- Jastreboff et al. (2023) — Retatrutide for obesity, phase 2 trial
Phase 2 obesity trial: studied regimens, weight and adverse events. Trial doses are not instructions for personal use.
Relevant sections: What this calculator does — and does not do · How trial doses relate to this
- DailyMed — Bacteriostatic Water for Injection, USP prescribing label
Product-specific composition, warnings and compatibility requirements. It does not authorize reconstitution of unapproved compounds.
Relevant sections: Why diluent volume is a choice, not a rule
- Health Canada (2026) — unauthorized injectable peptides bought online
Canadian safety and authorization notice for the products described. It does not establish approval status in every country.
Relevant sections: The legal and quality context
FAQ
How much bacteriostatic water do you add to a 10 mg retatrutide vial?+
There is no single answer — it is a concentration choice. 1 mL gives 10 mg/mL, 2 mL gives 5 mg/mL, 3 mL gives 3.33 mg/mL. The calculator shows what volume any amount corresponds to at each concentration.
How many units is 1 mg of retatrutide?+
It depends entirely on the concentration. At 5 mg/mL (10 mg in 2 mL), 1 mg is 0.2 mL, which is 20 units on a U-100 syringe. At 10 mg/mL it is 10 units. A units figure without a stated concentration is meaningless.
Is this a retatrutide dosing chart?+
No. Retatrutide has no approved dose. This page computes concentration and volume for numbers you enter; the trial regimens and their results are described, not prescribed, on the dosing guide.
What is a U-100 syringe unit in mL?+
0.01 mL. 100 units equals 1 mL. Units measure volume, not peptide mass.
Does adding more water make the retatrutide weaker?+
It lowers the concentration but not the total amount in the vial. The same mass is spread over more volume, so any given amount corresponds to a larger draw.