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How-to · reconstitution
Put 1 mL of bacteriostatic water into the 10 mg Tirzepatide vial. That makes 10.00 mg/mL. A 2.5 mg dose is then 25.0 units on a U-100 syringe.
That volume is the one that lands the draw on a syringe line, so the reading can be checked by eye. More water makes a weaker mix and a bigger draw. Less water makes a stronger mix and a smaller one. The amount of Tirzepatide in the glass never changes. Only the number of marks it takes does.
Tirzepatide is the drug in Zepbound and Mounjaro. It works on two gut hormone signals involved in appetite and blood sugar.
| Water added | Concentration | Per U-100 unit | Example: 2.5 mg = |
|---|---|---|---|
| 1 mL | 10.00 mg/mL | 100 mcg | 25.0 units |
| 2 mL | 5.00 mg/mL | 50 mcg | 50.0 units |
| 3 mL | 3.33 mg/mL | 33.33 mcg | 75.0 units |
Straight arithmetic: concentration = 10 mg ÷ water, and 1 U-100 unit = 0.01 mL. The example column shows the math at 2.5 mg; it is not a dose recommendation.
Which volume to use is a practical choice rather than a dose. Pick the one that puts your draw somewhere you can actually read it on the syringe. The flags in the last column mark where that fails. “Hard to measure” means the draw is too small to judge by eye. “Won’t fit” means it is bigger than one U-100 syringe holds.
The table above uses one worked example. These are the published quantities, converted into marks on a U-100 barrel at each water volume for a 10 mg vial. Where a quantity was never studied by injection, the row says so.
2.5 mg once weekly for 4 weeks, under the skin.
| Water added | Concentration | Draw |
|---|---|---|
| 1 mL | 10.00 mg/mL | 25.0 units |
| 2 mL | 5.00 mg/mL | 50.0 units |
| 3 mL | 3.33 mg/mL | 75.0 units |
FDA labelZepbound (tirzepatide) — FDA-approved Prescribing Information · retrieved 2026-07-22
5–15 mg once weekly, under the skin. (5, 10, or 15 mg).
| Water added | Concentration | Draw, low to high |
|---|---|---|
| 1 mL | 10.00 mg/mL | 50.0 to 150.0 unitswon’t fit |
| 2 mL | 5.00 mg/mL | 100.0 to 300.0 unitswon’t fit |
| 3 mL | 3.33 mg/mL | 150.0 to 450.0 unitswon’t fit |
FDA labelZepbound (tirzepatide) — FDA-approved Prescribing Information · retrieved 2026-07-22
Four doses at the amount shown, and the cited storage window is also four weeks. This is the only tirzepatide size where the vial and storage window end at the same time.
On every larger vial in this family the mixed solution expires with powder still in it. On the smaller one the powder runs out early and the window never binds.
This size lands on the line. There is no wastage to price in and no half-used vial to decide about, which is a genuinely different situation from its neighbors.
Every listed water amount puts the worked dose exactly on a syringe line. The other tirzepatide vial sizes each have at least one combination that falls between lines.
It means the choice on this page is only about how much liquid goes under the skin, never about whether the reading can be trusted.
Mixing guides converge on this vial, and the arithmetic explains why rather than taste. A vial that empties exactly as its window shuts needs no wastage sum and forces no rounding compromise.
That is a property of this vial at this amount, though, not a property of the vial. Move up the schedule and the four doses become one.
The table shows the offered water volumes. The calculator does the same arithmetic for any volume and any syringe, and shows its working line by line.
Open the Tirzepatide calculator →The arithmetic on this page is only half the question. These are the pages that carry the other half.