Tools
Tirzepatide reconstitution calculator
Reviewed September 2026
Quick answer
Concentration = milligrams in the vial ÷ milliliters of water added. A 10 mg vial mixed with 2 mL is 5 mg/mL. From there, a dose in milligrams divided by that concentration, times 100, is the mark on a U-100 syringe: 2.5 mg at 5 mg/mL is 50 units. The amount of water is not yours to choose; it comes from the pharmacy label or your prescriber, and so does the dose.
Your vial and your instructions
The total printed on the vial’s label, such as 10 mg. Not the dose, and not a per-mL figure.
The volume your pharmacy or prescriber told you to add. This tool does not pick it.
The number your prescriber set. Leave it empty to see only the concentration.
Concentration after mixing
Enter the milligrams on the vial and the milliliters of water added. The concentration appears here, and the syringe mark too if you add your dose.
Arithmetic only. It assumes the whole volume of water went into the vial and the powder fully dissolved. If your vial’s label or your prescriber’s instructions give a different figure, theirs is the one to follow.
How much bacteriostatic water for a 10 mg vial?
As much as your instructions say, and no chart can stand in for them. What a chart can show is what each choice does. The same 10 mg becomes a different strength with each volume, and every syringe mark after that follows from the strength.
| Vial | + 1 mL | + 2 mL | + 3 mL |
|---|---|---|---|
| 10 mg | 10 mg/mL | 5 mg/mL | 3.33 mg/mL |
| 15 mg | 15 mg/mL | 7.5 mg/mL | 5 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 |
| 60 mg | 60 mg/mL | 30 mg/mL | 20 mg/mL |
How many units at each strength
Once you know your concentration, this is the syringe mark for each of the label’s dose steps. Find your prescribed dose, then the column for your vial. The rows are the steps printed in the Zepbound label; the columns are example strengths, because a compounding pharmacy sets its own.1
| Dose | 5 mg/mL | 10 mg/mL | 15 mg/mL | 20 mg/mL |
|---|---|---|---|---|
| 2.5 mg | 50 units | 25 units | 16.7 units | 12.5 units |
| 5 mg | 100 units | 50 units | 33.3 units | 25 units |
| 7.5 mg | over 1 mL | 75 units | 50 units | 37.5 units |
| 10 mg | over 1 mL | 100 units | 66.7 units | 50 units |
| 12.5 mg | over 1 mL | over 1 mL | 83.3 units | 62.5 units |
| 15 mg | over 1 mL | over 1 mL | 100 units | 75 units |
Already know the concentration printed on your vial? Go straight to dose in units. For what the numbers mean, see tirzepatide dosage in units.
Why Zepbound needs none of this
The approved product arrives mixed. Zepbound’s label describes it as a “clear, colorless to slightly yellow solution” in single-dose pens, single-dose vials, multi-dose vials and KwikPens. Its multi-dose vial runs from 10 mg in 2.4 mL (4.17 mg/mL) to 60 mg in 2.4 mL (25 mg/mL), four 0.6 mL doses each.1
With a compounded vial, the strength is the pharmacy’s choice, and mixing ingredients to a prescription is the pharmacist’s job by FDA’s own definition of compounding.3 If you were handed a powder and a volume of water to add, the pharmacy that supplied them is the right place to confirm both before the first draw.
Questions
- How much bacteriostatic water do you add to 10 mg of tirzepatide?
- The volume is whatever the pharmacy that dispensed the vial, or your prescriber, tells you to add. It is not something to pick from a chart, because the volume sets the concentration and the concentration sets every syringe mark after it. The arithmetic for a 10 mg vial: 1 mL makes 10 mg/mL, 2 mL makes 5 mg/mL and 3 mL makes about 3.33 mg/mL.
- What concentration is 30 mg of tirzepatide with 3 mL of water?
- 10 mg/mL: 30 mg divided by 3 mL. With 2 mL the same vial is 15 mg/mL, and with 1 mL it is 30 mg/mL. Whichever volume your instructions give, the syringe marks for every dose follow from that one number.
- How do you calculate tirzepatide units from milligrams?
- Divide the dose in milligrams by the vial's concentration in mg/mL to get milliliters, then multiply by 100 to get units on a U-100 insulin syringe. If the vial was mixed from powder, the concentration is first the milligrams in the vial divided by the milliliters of water added.
- Does adding more water make the tirzepatide weaker?
- It makes each milliliter weaker, not the dose. The same milligrams are spread through more liquid, so the same dose takes more units on the syringe. That is why a mark that was right for one vial can be wrong for the next.
- Is it legal to buy tirzepatide powder and mix it yourself?
- Not as a research product. FDA says tirzepatide sold as “for research purposes” or “not for human consumption” is sold illegally, is of unknown quality and may be harmful. No approved tirzepatide is a powder: Zepbound and Mounjaro are supplied as solutions.