BAC Water Calculator
The amount of bacteriostatic water you add sets the concentration but never changes the total peptide in the vial. Concentration equals vial milligrams divided by millilitres of water. Adding more water means a lower concentration and more syringe units for the same dose, which makes small doses easier to measure precisely.
The formula
concentration mg/mL = vial mg ÷ BAC water mL
Because the peptide mass is fixed, this is a simple inverse relationship: double the water and you halve the concentration, which doubles the units you draw for any given dose.
Calculate your dose
Enter your vial and dose to see the units to draw.
- Concentration
- 5 mg/mL
- Volume to draw
- 0.1 mL
- Per unit
- 50 mcg
- Doses per vial
- 10
Worked examples
How the same vial behaves with different volumes of bacteriostatic water.
5 mg vial + 1 mL
10units
- Concentration
- 5 mg/mL
- Dose
- 0.5 mg
- Volume
- 0.1 mL
5 mg vial + 2 mL
20units
- Concentration
- 2.5 mg/mL
- Dose
- 0.5 mg
- Volume
- 0.2 mL
10 mg vial + 2 mL
20units
- Concentration
- 5 mg/mL
- Dose
- 1 mg
- Volume
- 0.2 mL
10 mg vial + 5 mL
50units
- Concentration
- 2 mg/mL
- Dose
- 1 mg
- Volume
- 0.5 mL
Frequently asked questions
- How much bacteriostatic water should I use?
- Arithmetically any volume works, since the peptide mass is unchanged. Larger volumes give more syringe units per dose, which reduces measurement error on small doses. Follow the instructions supplied with your vial or from your prescriber.
- Does more bacteriostatic water weaken the peptide?
- It lowers the concentration, not the total amount. Drawing the correct number of units at the new concentration delivers exactly the same milligrams.
- How much BAC water for a 10 mg vial?
- 1 mL gives 10 mg/mL, 2 mL gives 5 mg/mL, and 5 mL gives 2 mg/mL. At 2 mg/mL a 1 mg dose is 0.5 mL, or 50 units on a U-100 syringe.
- Can I add more water to an already-reconstituted vial?
- Doing so changes the concentration, so every previously calculated unit figure becomes wrong and must be recalculated. Handling and sterility questions are outside the scope of this arithmetic — consult your prescriber.
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