How much bacteriostatic water do I add to a 20 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 20 mg vial is 10 mg/mL, so every 10 units on a U-100 insulin syringe holds 1 mg. With 1 mL it is 20 mg/mL (2 mg per 10 units). With 3 mL it is 6.67 mg/mL (666.667 mcg per 10 units). With 5 mL it is 4 mg/mL (400 mcg per 10 units).

How many units is 2.5 mg of tirzepatide from a 20 mg vial?

With 2 mL of water the vial is 10 mg/mL, so 2.5 mg is 0.25 mL, or 25 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 20 mg tirzepatide vial?

8 (20 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 20 mg Reconstitution: BAC Water & Units

Short answer: 2 mL of bacteriostatic water in a 20 mg tirzepatide vial makes 10 mg/mL. On a U-100 insulin syringe (1 mL = 100 units), every 10 units then holds 1 mg. More water gives a weaker solution and a bigger draw for the same amount; the amount in the vial stays 20 mg.

Water volume chart for a 20 mg vial

20 mg tirzepatide vial, U-100 insulin syringe.
Water added	Concentration	Per 10 units	Per 1 unit
1 mL	20 mg/mL	2 mg	200 mcg
2 mL	10 mg/mL	1 mg	100 mcg
3 mL	6.67 mg/mL	666.667 mcg	66.667 mcg
5 mL	4 mg/mL	400 mcg	40 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 20 mg vial.
Water added	1.25 mg	2.5 mg	5 mg
1 mL	6.3 units	12.5 units	25 units
2 mL	12.5 units	25 units	50 units
3 mL	18.8 units	37.5 units	75 units
5 mL	31.3 units	62.5 units	over 1 mL

A 20 mg vial holds 16 draws of 1.25 mg, 8 draws of 2.5 mg, 4 draws of 5 mg, no matter how much water you add.

The math

Concentration. 20 mg ÷ 2 mL = 10 mg/mL
Volume to draw. amount ÷ 10 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 15 mg · Tirzepatide 30 mg

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

Tirzepatide 20 mg reconstitution: how much water and how many units

Water volume chart for a 20 mg vial

Syringe units by amount

The math

Other tirzepatide vial sizes

Frequently asked questions