How much bacteriostatic water do I add to a 15 mg semaglutide 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 250 mcg of semaglutide from a 15 mg vial?

With 2 mL of water the vial is 7.5 mg/mL, so 250 mcg is 0.033 mL, or 3.3 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 250 mcg draws are in a 15 mg semaglutide vial?

60 (15 mg ÷ 250 mcg), whatever volume of water you add. In practice a little is lost to the syringe dead space and the last drops in the vial.

Semaglutide 15 mg Reconstitution: BAC Water & Units

Short answer: 2 mL of bacteriostatic water in a 15 mg semaglutide 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 semaglutide 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	125 mcg	250 mcg	500 mcg
1 mL	under 2 units	under 2 units	3.3 units
2 mL	under 2 units	3.3 units	6.7 units
3 mL	2.5 units	5 units	10 units
5 mL	4.2 units	8.3 units	16.7 units

A 15 mg vial holds 120 draws of 125 mcg, 60 draws of 250 mcg, 30 draws of 500 mcg, no matter how much water you add.

How far a 15 mg vial goes

Draws per vial depend only on the amount per draw, not on the water. The volume and units columns use 2 mL of water (7.5 mg/mL). Example amounts only, not doses.

15 mg vial: draws, volume and units per example amount.
Amount per draw	Draws per vial	Volume per draw	Units per draw
62.5 mcg	240	0.008 mL	under 2 units
125 mcg	120	0.017 mL	under 2 units
250 mcg	60	0.033 mL	3.3 units
500 mcg	30	0.067 mL	6.7 units
1 mg	15	0.133 mL	13.3 units

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

15 mg next to other semaglutide vial sizes

To get the same 7.5 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 7.5 mg/mL, and 250 mcg draws per vial, by vial size.
Vial	Water for 7.5 mg/mL	250 mcg draws per vial
2 mg	0.27 mL	8
3 mg	0.4 mL	12
5 mg	0.67 mL	20
10 mg	1.33 mL	40
15 mg (this page)	2 mL	60
20 mg	2.67 mL	80

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 semaglutide vial sizes: Semaglutide 2 mg · Semaglutide 3 mg · Semaglutide 5 mg · Semaglutide 10 mg · Semaglutide 20 mg

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

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