How much bacteriostatic water do I add to a 3 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 3 mg vial is 1.5 mg/mL, so every 10 units on a U-100 insulin syringe holds 150 mcg. With 1 mL it is 3 mg/mL (300 mcg per 10 units). With 3 mL it is 1 mg/mL (100 mcg per 10 units). With 5 mL it is 600 mcg/mL (60 mcg per 10 units).

How many units is 250 mcg of semaglutide from a 3 mg vial?

With 2 mL of water the vial is 1.5 mg/mL, so 250 mcg is 0.167 mL, or 16.7 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 3 mg semaglutide vial?

12 (3 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 3 mg Reconstitution: BAC Water & Units

Short answer: 2 mL of bacteriostatic water in a 3 mg semaglutide vial makes 1.5 mg/mL. On a U-100 insulin syringe (1 mL = 100 units), every 10 units then holds 150 mcg. More water gives a weaker solution and a bigger draw for the same amount; the amount in the vial stays 3 mg.

Water volume chart for a 3 mg vial

3 mg semaglutide vial, U-100 insulin syringe.
Water added	Concentration	Per 10 units	Per 1 unit
1 mL	3 mg/mL	300 mcg	30 mcg
2 mL	1.5 mg/mL	150 mcg	15 mcg
3 mL	1 mg/mL	100 mcg	10 mcg
5 mL	600 mcg/mL	60 mcg	6 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 3 mg vial.
Water added	125 mcg	250 mcg	500 mcg
1 mL	4.2 units	8.3 units	16.7 units
2 mL	8.3 units	16.7 units	33.3 units
3 mL	12.5 units	25 units	50 units
5 mL	20.8 units	41.7 units	83.3 units

A 3 mg vial holds 24 draws of 125 mcg, 12 draws of 250 mcg, 6 draws of 500 mcg, no matter how much water you add.

How far a 3 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 (1.5 mg/mL). Example amounts only, not doses.

3 mg vial: draws, volume and units per example amount.
Amount per draw	Draws per vial	Volume per draw	Units per draw
62.5 mcg	48	0.042 mL	4.2 units
125 mcg	24	0.083 mL	8.3 units
250 mcg	12	0.167 mL	16.7 units
500 mcg	6	0.333 mL	33.3 units
1 mg	3	0.667 mL	66.7 units

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

3 mg next to other semaglutide vial sizes

To get the same 1.5 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 1.5 mg/mL, and 250 mcg draws per vial, by vial size.
Vial	Water for 1.5 mg/mL	250 mcg draws per vial
2 mg	1.33 mL	8
3 mg (this page)	2 mL	12
5 mg	3.33 mL	20
10 mg	6.67 mL	40
15 mg	10 mL	60
20 mg	13.33 mL (over 10 mL)	80

The math

Concentration. 3 mg ÷ 2 mL = 1.5 mg/mL
Volume to draw. amount ÷ 1.5 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 5 mg · Semaglutide 10 mg · Semaglutide 15 mg · Semaglutide 20 mg

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

Semaglutide 3 mg reconstitution: how much water and how many units