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Tirzepatide Reconstitution: The Chart and the Math Behind It
One division determines every dose you draw afterwards. Here is the chart, and the reasoning that produces it.
Peptide Library Editorial · October 21, 2026 · 3 min read
Reconstitution is one division, and it determines everything downstream. Concentration equals vial mass divided by the volume of bacteriostatic water added. Every dose drawn afterwards is that concentration multiplied by a volume.
Approved tirzepatide comes ready to use. Mounjaro and Zepbound are supplied as solutions in pens or single-dose vials and are not reconstituted. This page covers the arithmetic for lyophilised research vials, which are a different product entirely and are not approved for human use.
The chart
Concentration in mg/mL for the common vial sizes, by volume of bacteriostatic water added:
Vial | 1 mL | 2 mL | 3 mL | 4 mL | 5 mL |
|---|---|---|---|---|---|
5 mg | 5.0 mg/mL | 2.5 mg/mL | 1.67 mg/mL | 1.25 mg/mL | 1.0 mg/mL |
10 mg | 10 mg/mL | 5.0 mg/mL | 3.33 mg/mL | 2.5 mg/mL | 2.0 mg/mL |
15 mg | 15 mg/mL | 7.5 mg/mL | 5.0 mg/mL | 3.75 mg/mL | 3.0 mg/mL |
20 mg | 20 mg/mL | 10 mg/mL | 6.67 mg/mL | 5.0 mg/mL | 4.0 mg/mL |
30 mg | 30 mg/mL | 15 mg/mL | 10 mg/mL | 7.5 mg/mL | 6.0 mg/mL |
40 mg | 40 mg/mL | 20 mg/mL | 13.3 mg/mL | 10 mg/mL | 8.0 mg/mL |
Volume to draw, in syringe units
A U-100 insulin syringe is marked in units where 100 units is 1 mL, so one unit is 0.01 mL. Units to draw for a target dose:
Concentration | 2.5 mg | 5 mg | 7.5 mg | 10 mg | 15 mg |
|---|---|---|---|---|---|
2.5 mg/mL | 100 u | — | — | — | — |
5 mg/mL | 50 u | 100 u | — | — | — |
10 mg/mL | 25 u | 50 u | 75 u | 100 u | — |
15 mg/mL | 17 u | 33 u | 50 u | 67 u | 100 u |
20 mg/mL | 12.5 u | 25 u | 37.5 u | 50 u | 75 u |
Choose the reconstitution volume so that doses land between 10 and 50 units. Below about 5 units the marking error is a large fraction of the dose; above 50 you are using more vial volume than necessary. If a dose falls outside that band, change the water volume rather than trying to read between markings. The peptide calculator solves for this directly.
Worked example
A 30 mg vial, reconstituted with 3 mL of bacteriostatic water:
Concentration: 30 mg ÷ 3 mL = 10 mg/mL.
For a 5 mg dose: 5 mg ÷ 10 mg/mL = 0.5 mL = 50 units.
For a 2.5 mg dose: 2.5 mg ÷ 10 mg/mL = 0.25 mL = 25 units.
Doses per vial: 30 mg ÷ 5 mg = 6 doses at 5 mg.
Time in use: six weekly doses is six weeks — which exceeds the 28-day limit on bacteriostatic water, and is the constraint most people miss.
That last step is the one that catches people out. A vial holding more doses than 28 days allows is not a bargain. The bacteriostatic water guide covers where the 28-day figure comes from — it is a property of the 0.9% benzyl alcohol preservative, not of the peptide.
Procedure
Let the vial reach room temperature before adding anything.
Swab both stoppers and allow them to dry.
Add the water down the vial wall, slowly. Directing the stream onto the powder can shear the peptide.
Do not shake. Swirl gently, or let it dissolve undisturbed.
Inspect. The solution should be clear and free of particulates. Cloudiness or visible material means stop.
Label with the date and the resulting concentration, not just the vial mass.
Refrigerate at 2–8 °C, protected from light.
The full reconstitution guide covers the procedure in more depth, and the storage guide covers what happens afterwards.
Common errors
Error | Consequence |
|---|---|
Labelling the vial with mg instead of mg/mL | Concentration is lost; later doses become guesses |
Assuming units equal milligrams | Units are volume — a 100-fold class of error |
Reusing a familiar water volume for a different vial size | Concentration changes silently |
Shaking to dissolve faster | Mechanical stress on the peptide |
Adding water to a cold vial | Slower dissolution, more handling |
Ignoring the 28-day limit | Preservative efficacy expires before the vial does |
The units-to-mL guide covers the second row in detail, and the peptide cheat sheet collects all of these conversions on one page.
Research and educational use only. Peptide Library is an independent research and comparison platform and does not sell peptides. Nothing here is medical advice, dosing guidance, or a recommendation to administer any substance to a person or an animal. Consult a licensed clinician for anything concerning human health.
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Peptide Library Editorial
Editorial content from Peptide Library. Research and educational use only. Not medical advice.
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