For a 10 mg retatrutide vial reconstituted with 1 mL of bacteriostatic water, the concentration works out to 10 mg/mL, so a 2 mg dose measures as 0.2 mL, which reads as 20 units on a standard U-100 insulin syringe. The calculator below runs that same math, concentration first, then volume to draw, then units, for any vial strength, water volume and dose you enter. Retatrutide is investigational, so this is reconstitution arithmetic for educational reference, not a recommendation to prepare or administer anything.
Retatrutide is an investigational drug. It is not FDA-approved for human use and cannot legally be prescribed or bought. This page performs reconstitution arithmetic for educational purposes only: it is not medical advice and not a directive to prepare or administer anything. Always consult a licensed clinician before considering any GLP-1 therapy. See our Affiliate Disclosure.
Retatrutide reconstitution calculator
Enter the peptide amount in the vial, the bacteriostatic water added, and a target dose. The calculator returns the concentration, the volume to draw, and the units on a standard U-100 insulin syringe, the same three-step arithmetic explained below.
A U-100 insulin syringe has 100 units per 1 mL, so units = volume to draw × 100. Adding more water lowers the concentration and raises the units needed for the same dose.
How the reconstitution math works
Retatrutide reconstitution math is three steps: concentration, then volume, then units. Concentration in milligrams per milliliter equals the total milligrams of peptide in the vial divided by the milliliters of bacteriostatic water added. Volume to draw equals the desired dose divided by that concentration. Units on a U-100 insulin syringe, the standard syringe for measurements this small, equal the volume in milliliters multiplied by 100, since a U-100 syringe holds 100 units per milliliter.
Worked example: a 10 mg vial mixed with 1 mL of bacteriostatic water gives a concentration of 10 mg divided by 1 mL, or 10 mg/mL. A 2 mg dose at that concentration is 2 mg divided by 10 mg/mL, which equals 0.2 mL, and 0.2 mL on a U-100 syringe reads as 20 units. The same two-step math, concentration first, then volume to draw, applies to any vial size and any water volume, which is exactly what the calculator above automates. The total peptide in the vial never changes: adding more water only spreads it across more liquid, so each unit on the syringe ends up holding less.
Concentration by vial size and water volume
The table below works the same arithmetic across the three vial sizes and three bacteriostatic water volumes people search for most. Each cell is the resulting concentration in milligrams per milliliter; divide any dose by that number to get the volume to draw, then multiply by 100 for units on a U-100 syringe.
| Vial size | 1 mL BAC water | 2 mL BAC water | 3 mL BAC water |
|---|---|---|---|
| 10 mg | 10 mg/mL | 5 mg/mL | 3.33 mg/mL |
| 20 mg | 20 mg/mL | 10 mg/mL | 6.67 mg/mL |
| 30 mg | 30 mg/mL | 15 mg/mL | 10 mg/mL |
Adding more bacteriostatic water lowers the concentration and raises the volume needed for the same dose, which is why the 3 mL column produces a lower mg/mL number than the 1 mL column in every row. A 20 mg vial mixed with 2 mL, for example, also lands on 10 mg/mL, the same concentration as a 10 mg vial mixed with 1 mL, which is why 10 mg/mL shows up more than once in the table. For the trial’s own dose-escalation schedule and weight-loss results by dose, see the full retatrutide dosage guide.
Storage after reconstitution
Because retatrutide has no FDA approval, there is no manufacturer storage label for a reconstituted vial, so any specific shelf-life figure quoted online is not sourced from an approved product insert. General handling guidance published for comparable reconstituted peptides points toward refrigeration rather than room temperature once bacteriostatic water has been added, since introducing water and a preservative to a lyophilized, freeze-dried powder starts a slow degradation process that heat accelerates. Before reconstitution, lyophilized peptide powder is comparatively stable and is typically kept refrigerated or frozen, per general peptide-handling literature.
That same general guidance points to a few practices that are not specific to any single compound: mix by gently swirling or rolling the vial rather than shaking it, since vigorous agitation can physically damage a protein structure; keep the vial away from direct light, which is why amber or foil-wrapped packaging is common; and avoid repeated freeze-thaw cycles, each of which stresses the dissolved peptide more than one stable refrigeration period. A solution that has turned cloudy or changed color from its original appearance is a standard discard signal across peptide-handling guidance generally, not a retatrutide-specific finding, since no clinical trial has published its own stability data for at-home storage.
Source
Retatrutide’s investigational status, and every clinical figure referenced elsewhere on this site, trace back to Jastreboff AM, Kaplan LM, Frías JP, et al., “Triple-Hormone-Receptor Agonist Retatrutide for Obesity, A Phase 2 Trial,” New England Journal of Medicine, 2023;389(6):514-526, DOI: 10.1056/NEJMoa2301972, PMID 37366315, registered as ClinicalTrials.gov NCT04881760. This calculator itself performs standard pharmacy arithmetic and does not depend on any specific trial figure. For the full dose-by-dose trial results and titration schedule, see the retatrutide guide and the dosage guide.
Reconstitution calculator: frequently asked questions
How much bacteriostatic water do you use for a 10 mg vial?
It depends on the concentration you’re solving for: 1 mL of bacteriostatic water into a 10 mg vial yields 10 mg/mL, so a 2 mg dose measures as 0.2 mL, or 20 units on a U-100 syringe. 2 mL yields 5 mg/mL instead, doubling the volume needed for the same dose.
How do you calculate retatrutide units on an insulin syringe?
Divide the vial strength by the bacteriostatic water added to get the concentration in mg/mL, divide the desired dose by that concentration to get the volume in mL, then multiply by 100 for units on a U-100 syringe. The calculator above runs this automatically.
Does adding more bacteriostatic water change the dose?
No. It changes the concentration, not the total peptide in the vial. More water spreads the same amount of retatrutide across a larger volume, so each unit on the syringe holds less, and a given dose needs more units to reach it.
What is a U-100 syringe?
A U-100 insulin syringe holds 100 units per milliliter, the standard syringe used for the small volumes this kind of reconstitution math produces. Units equal the volume to draw in milliliters multiplied by 100.
How much bacteriostatic water for a 20 mg vial?
1 mL yields 20 mg/mL, 2 mL yields 10 mg/mL, and 3 mL yields about 6.67 mg/mL. The worked table above covers 10, 20 and 30 mg vials against all three common water volumes.
Does retatrutide need to be refrigerated after reconstitution?
There is no FDA-approved label to answer that definitively, since retatrutide itself is not approved. General handling guidance for comparable reconstituted peptides points to refrigeration and protection from light once bacteriostatic water has been added.
Can you buy retatrutide to use with this calculator?
No. Retatrutide is investigational and cannot legally be bought or prescribed. This calculator is reconstitution arithmetic for educational reference only. See our retatrutide guide for the full picture, including what is available by prescription today.
Is this calculator giving medical or dosing advice?
No. It performs arithmetic, concentration, volume and units, based on the numbers you enter. It is not a recommendation for a specific dose, and retatrutide has no FDA-approved dosing label for any clinician to prescribe from.