Reconstitution tool
BAC Water Calculator: Pick the Right Mix Volume
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How do I pick the right BAC water volume for a peptide vial?
Pick a bacteriostatic water volume so your typical dose lands between 10 and 50 units on a U-100 insulin syringe — readable without micropipetting. For a 5 mg vial with a 250 mcg target dose, 2 ml of BAC water gives 2.5 mg/ml and a clean 10-unit draw. Adding more BAC water dilutes the concentration; the total mass in the vial is unchanged.
The math
- Concentration = vial mass (mg) ÷ BAC water (ml).
- Draw volume = target dose ÷ concentration.
- U-100 units = draw volume (ml) × 100.
BAC water volume vs unit count (5 mg vial example)
| Vial | BAC water | Concentration | Example dose | U-100 units |
|---|---|---|---|---|
| 5 mg | 1 ml | 5 mg/ml | 250 mcg | 5 units |
| 5 mg | 2 ml | 2.5 mg/ml | 250 mcg | 10 units |
| 5 mg | 3 ml | 1.67 mg/ml | 250 mcg | 15 units |
| 5 mg | 4 ml | 1.25 mg/ml | 250 mcg | 20 units |
| 5 mg | 5 ml | 1 mg/ml | 250 mcg | 25 units |
How Peptly helps you pick
Peptly shows the unit count live as you adjust the BAC slider. Set your target dose first, then move the BAC slider until the unit count lands in a range you can read without squinting. The saved reconstitution mix locks in the choice so you do not re-derive it on every dose.
Practical readability rule of thumb
- 5–15 units — works for any dose; useful for precise small doses.
- 10–50 units — easy to read on a standard U-100 syringe scale.
- 50–100 units — fine, but takes up most of a U-100 syringe.
- >100 units — exceeds a single U-100 syringe; consider a higher concentration (less BAC water).
See also
Frequently asked questions
What is bacteriostatic water? +
Bacteriostatic water for injection (BWFI) is sterile water with 0.9% benzyl alcohol as a preservative. The benzyl alcohol inhibits microbial growth, making the water suitable for multi-use vials over a 28-day window after opening.
How much BAC water should I add to a vial? +
There is no single correct volume — it is a readability choice. Pick a BAC volume so that your typical dose lands between 10 and 50 units on a U-100 syringe — easy to read without micropipetting. Peptly shows the unit count for any combination live.
Does adding more BAC water mean a weaker peptide? +
No. The total peptide mass in the vial is unchanged. Adding more BAC water means a lower concentration (mg/ml), so you draw more volume (more units) for the same mass dose. The mass per dose stays the same.
Can I use sterile water instead of BAC water? +
Sterile water (without preservative) is suitable for single use but not for multi-day storage of reconstituted vials. BAC water is the standard for any vial used over more than one injection.
How long does BAC water last after opening? +
Per the standard label, BAC water is suitable for use within 28 days of opening when stored at 2–8 °C. Always follow the manufacturer label and consult primary sources.