How much bacteriostatic water do I add to a 15 mg tirzepatide vial?

There is no single right amount. More water makes each draw bigger and easier to measure; less water keeps the volume small. With 2 mL, a 15 mg vial is 7.5 mg/mL, so every 10 units on a U-100 insulin syringe holds 750 mcg. With 1 mL it is 15 mg/mL (1.5 mg per 10 units). With 3 mL it is 5 mg/mL (500 mcg per 10 units). With 5 mL it is 3 mg/mL (300 mcg per 10 units).

How many units is 2.5 mg of tirzepatide from a 15 mg vial?

With 2 mL of water the vial is 7.5 mg/mL, so 2.5 mg is 0.333 mL, or 33.3 units on a U-100 syringe. With a different water volume the units change but the amount does not. The amount is an example for the math, not a recommendation.

How many 2.5 mg draws are in a 15 mg tirzepatide vial?

6 (15 mg ÷ 2.5 mg), whatever volume of water you add. In practice a little is lost to the syringe dead space and the last drops in the vial.

Tirzepatide 15 mg Reconstitution: BAC Water & Units

Short answer: 2 mL of bacteriostatic water in a 15 mg tirzepatide vial makes 7.5 mg/mL. On a U-100 insulin syringe (1 mL = 100 units), every 10 units then holds 750 mcg. More water gives a weaker solution and a bigger draw for the same amount; the amount in the vial stays 15 mg.

Water volume chart for a 15 mg vial

15 mg tirzepatide vial, U-100 insulin syringe.
Water added	Concentration	Per 10 units	Per 1 unit
1 mL	15 mg/mL	1.5 mg	150 mcg
2 mL	7.5 mg/mL	750 mcg	75 mcg
3 mL	5 mg/mL	500 mcg	50 mcg
5 mL	3 mg/mL	300 mcg	30 mcg

Syringe units by amount

The amounts below are examples to show the conversion, not doses. How much to take is a decision for you and your prescriber.

Units on a U-100 syringe from a 15 mg vial.
Water added	1.25 mg	2.5 mg	5 mg
1 mL	8.3 units	16.7 units	33.3 units
2 mL	16.7 units	33.3 units	66.7 units
3 mL	25 units	50 units	100 units
5 mL	41.7 units	83.3 units	over 1 mL

A 15 mg vial holds 12 draws of 1.25 mg, 6 draws of 2.5 mg, 3 draws of 5 mg, no matter how much water you add.

The math

Concentration. 15 mg ÷ 2 mL = 7.5 mg/mL
Volume to draw. amount ÷ 7.5 mg/mL = mL
Syringe units. mL × 100 = units

For a different water volume or amount, the free peptide reconstitution calculator works backwards from the amount you want and suggests a water volume that lands on a clean syringe mark.

Other tirzepatide vial sizes

Tirzepatide 5 mg · Tirzepatide 10 mg · Tirzepatide 20 mg · Tirzepatide 30 mg

Half-life, time to peak and sources are on the main Tirzepatide guide.

Tirzepatide 15 mg reconstitution: how much water and how many units

Water volume chart for a 15 mg vial

Syringe units by amount

The math

Other tirzepatide vial sizes

Frequently asked questions