How much bacteriostatic water do I add to a 40 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 10 mL, a 40 mg vial is 4 mg/mL, so every 10 units on a U-100 insulin syringe holds 400 mcg. With 2 mL it is 20 mg/mL (2 mg per 10 units). With 3 mL it is 13.33 mg/mL (1.333 mg per 10 units). With 5 mL it is 8 mg/mL (800 mcg per 10 units).

How many units is 2.5 mg of tirzepatide from a 40 mg vial?

With 10 mL of water the vial is 4 mg/mL, so 2.5 mg is 0.625 mL, or 62.5 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 40 mg tirzepatide vial?

16 (40 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 40 mg Reconstitution: BAC Water & Units

Short answer: 10 mL of bacteriostatic water in a 40 mg tirzepatide vial makes 4 mg/mL. On a U-100 insulin syringe (1 mL = 100 units), every 10 units then holds 400 mcg. More water gives a weaker solution and a bigger draw for the same amount; the amount in the vial stays 40 mg.

Water volume chart for a 40 mg vial

40 mg tirzepatide vial, U-100 insulin syringe.
Water added	Concentration	Per 10 units	Per 1 unit
2 mL	20 mg/mL	2 mg	200 mcg
3 mL	13.33 mg/mL	1.333 mg	133.333 mcg
5 mL	8 mg/mL	800 mcg	80 mcg
10 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 40 mg vial.
Water added	1.25 mg	2.5 mg	5 mg
2 mL	6.3 units	12.5 units	25 units
3 mL	9.4 units	18.8 units	37.5 units
5 mL	15.6 units	31.3 units	62.5 units
10 mL	31.3 units	62.5 units	over 1 mL

A 40 mg vial holds 32 draws of 1.25 mg, 16 draws of 2.5 mg, 8 draws of 5 mg, no matter how much water you add.

How far a 40 mg vial goes

Draws per vial depend only on the amount per draw, not on the water. The volume and units columns use 10 mL of water (4 mg/mL). Example amounts only, not doses.

40 mg vial: draws, volume and units per example amount.
Amount per draw	Draws per vial	Volume per draw	Units per draw
625 mcg	64	0.156 mL	15.6 units
1.25 mg	32	0.313 mL	31.3 units
2.5 mg	16	0.625 mL	62.5 units
5 mg	8	1.25 mL	over 1 mL
10 mg	4	2.5 mL	over 1 mL

Real counts run a little lower: some liquid stays in the syringe and at the bottom of the vial.

40 mg next to other tirzepatide vial sizes

To get the same 4 mg/mL from another vial size, scale the water with the vial. Same strength means the same units for the same amount, whichever vial it comes from.

Water for 4 mg/mL, and 2.5 mg draws per vial, by vial size.
Vial	Water for 4 mg/mL	2.5 mg draws per vial
5 mg	1.25 mL	2
10 mg	2.5 mL	4
15 mg	3.75 mL	6
20 mg	5 mL	8
30 mg	7.5 mL	12
40 mg (this page)	10 mL	16
50 mg	12.5 mL (over 10 mL)	20
60 mg	15 mL (over 10 mL)	24

The math

Concentration. 40 mg ÷ 10 mL = 4 mg/mL
Volume to draw. amount ÷ 4 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 20 mg · Tirzepatide 30 mg · Tirzepatide 50 mg · Tirzepatide 60 mg

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

Tirzepatide 40 mg reconstitution: how much water and how many units