Does the amount of bacteriostatic water change my dose?

No. It changes how many units you draw, not how much peptide you receive. More water makes a weaker solution, so the same dose is a larger number of units on the syringe.

How much bacteriostatic water should I add to a peptide vial?

Use the exact product instructions and guidance from a qualified clinician or pharmacist. This calculator can show how a chosen volume changes the syringe mark, but it cannot decide which volume is appropriate.

What is the difference between bacteriostatic water and sterile water?

Bacteriostatic water contains benzyl alcohol as a preservative, which allows a vial to be entered more than once. Sterile water has no preservative and is intended for single use.

Why is an insulin syringe marked in units instead of millilitres?

Insulin syringes are marked for insulin dosing. The U-100 standard means 100 units per millilitre, so 0.5 mL is 50 units.

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Peptide reconstitution calculator

Enter the vial strength, how much bacteriostatic water you added, and the dose you want. You get the mark to draw to on a U-100 insulin syringe.

Peptide in vial (mg)

Bacteriostatic water added (mL)

Dose per injection

mg mcg

Syringe

Units to draw 5 mg/mL total
4 doses per vial

Common mixes

If you always mix the same way you only need to read this once. Every number is units on a U-100 syringe.

5 mg vial
Dose	1 mL water	2 mL water	3 mL water
0.25 mg	5	10	15
0.5 mg	10	20	30
1 mg	20	40	60
1.5 mg	30	60	90
2 mg	40	80	120
2.5 mg	50	100	150

10 mg vial
Dose	1 mL water	2 mL water	3 mL water
0.5 mg	5	10	15
1 mg	10	20	30
2 mg	20	40	60
2.5 mg	25	50	75
5 mg	50	100	150

5 mg vial, doses in micrograms
Dose	1 mL water	2 mL water	3 mL water
100 mcg	2	4	6
200 mcg	4	8	12
250 mcg	5	10	15
300 mcg	6	12	18
500 mcg	10	20	30

Anything over 100 will not fit in one 1 mL syringe. Use less water or a bigger barrel.

How the math works

Two steps, and the second one is where people slip up.

concentration = mg in vial / mL of water

mL to inject = dose in mg / concentration

units = mL to inject x 100

The multiply by 100 is the part that catches people. A U-100 syringe is marked in units, not millilitres, and 100 units is exactly 1 mL. So 0.25 mL is 25 units. Every U-100 syringe uses that same scale whether the barrel holds 0.3, 0.5 or 1 mL. A bigger barrel just means more units fit.

Worked example. A 10 mg vial with 2 mL of bacteriostatic water gives 5 mg per mL. You want 2.5 mg, so you need half a millilitre, which is 50 units. The vial holds four of those doses.

Questions people ask

Does the amount of water change my dose?: No. It changes how many units you draw, not how much peptide you get. More water means a weaker solution and a bigger number on the syringe for the same dose. Some people add extra water on purpose because small numbers are hard to measure.
How much water should I add?: Use the exact product instructions and guidance from a qualified clinician or pharmacist. This calculator can show how a chosen water volume changes the syringe mark, but it cannot decide which volume is appropriate.
What is the difference between bacteriostatic and sterile water?: Bacteriostatic water contains a small amount of benzyl alcohol, which stops bacterial growth and lets a vial be entered more than once. Sterile water has no preservative, so it is intended for a single use.
Why does my syringe say units instead of mL?: Insulin syringes are marked for insulin, which is dosed in international units. The U-100 standard means 100 units per millilitre. That is why every conversion here ends in a multiply by 100.
How long does a reconstituted vial last?: It depends on the compound, the storage temperature and whether you used a preserved diluent. Keep it cold and keep it out of light. The label and the supplier documentation are the only reliable source for a specific compound.

Worked it out once, then keep the record connected. VialTracker saves vial concentration, remaining volume, dose history, schedules, sites, and notes so the entered numbers are available next time.