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How-to · reconstitution
Put 3 mL of bacteriostatic water into the 15 mg Tirzepatide vial. That makes 5.00 mg/mL. A 2.5 mg dose is then 50.0 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 | 15.00 mg/mL | 150 mcg | 16.7 units |
| 2 mL | 7.50 mg/mL | 75 mcg | 33.3 units |
| 3 mL | 5.00 mg/mL | 50 mcg | 50.0 units |
Straight arithmetic: concentration = 15 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 15 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 | 15.00 mg/mL | 16.7 units |
| 2 mL | 7.50 mg/mL | 33.3 units |
| 3 mL | 5.00 mg/mL | 50.0 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 | 15.00 mg/mL | 33.3 to 100.0 units |
| 2 mL | 7.50 mg/mL | 66.7 to 200.0 unitswon’t fit |
| 3 mL | 5.00 mg/mL | 100.0 to 300.0 unitswon’t fit |
FDA labelZepbound (tirzepatide) — FDA-approved Prescribing Information · retrieved 2026-07-22
At the worked amount, this vial holds six doses while the stated mixed-vial window covers four. About one third of the powder would remain.
This is the first size on the tirzepatide ladder where that flips. Two doses’ worth of solution is still in the glass when the date arrives, and the date is what decides, not the volume left.
The mixing table cannot show this. It stops at concentration and draw, and says nothing about how long you have to use them.
Of the three listed, two drop the draw between syringe lines and one gives a whole number of units. On a draw this size a mark either way is a small share of the dose, so the difference is minor.
The exact figure stays visible because a silently rounded number is harder to verify.
The wastage above comes from pairing a large vial with the schedule’s opening amount. At the lowest maintenance step of the same schedule, this vial holds three doses and clears the window with nothing left over.
So the vial is not the mistake. Mixing it while still at the bottom of the schedule is.
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.