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How-to · reconstitution
In this example, 3 mL of bacteriostatic water in a 15 mg Tirzepatide vial gives 5.00 mg/mL. An example 2.5 mg amount is then 50.0 units on a U-100 syringe.
This example lands on a syringe line. More water makes a weaker mix and a bigger draw. Less water makes a stronger mix and a smaller one. The amount of Tirzepatide stays the same. Use the diluent and volume specified for your product; the arithmetic alone does not choose them.
| 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 ÷ liquid volume, and 1 U-100 unit = 0.01 mL. The example column shows the math at 2.5 mg; it is not a dose recommendation.
The table compares possible concentrations; it does not establish which diluent or volume suits your product. Follow its dispensing instructions.
“Hard to measure” means the example draw is below two U-100 units. “Won’t fit” means it exceeds this syringe’s capacity.
Tirzepatide is the drug in Zepbound and Mounjaro. It works on two gut hormone signals involved in appetite and blood sugar.
The table above uses one worked example. These are the published quantities, converted into marks on a U-100 barrel at each listed liquid 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 2026-09-19
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 2026-09-19
At the displayed dose, this vial divides into six complete doses. Only the largest of the three water amounts gives a whole-unit draw on the illustrated syringe.
The first two water amounts produce fractional units because the entered dose does not divide evenly at those concentrations. The last row gives a whole number. These differences come from the ratio of drug to liquid, not from a change in the dose.
Keep the calculated fraction visible while checking the result. Rounding it without checking the syringe changes the amount of drug represented by the reading.
The diagram uses a U-100 scale with whole-unit marks. Actual syringes can have different capacities and spacing between their lines. A reading that fits this drawing may not have a matching line on the syringe you have.
The suitable diluent and volume come from the product instructions. Do not change the mixture just to make a decimal disappear; ask the dispensing pharmacist to resolve a draw you cannot measure.
Six is the result of vial content divided by the worked dose, before losses. It says nothing about how long the solution remains suitable for use or how often a particular container may be entered.
This guide therefore does not assign an expiry date or predict discarded doses from the ingredient name. The product label supplies those limits. If the prescribed dose changes, recalculate the draw and remaining quantity using that new amount.
The calculator lets you enter your product’s vial strength and mixing volume, then shows the arithmetic for your syringe.
Open the Tirzepatide calculator →The arithmetic on this page is only half the question. These are the pages that carry the other half.