BAC Water Calculator for Peptides
Answers how much bacteriostatic water should I add? Enter your vial size and dose to get a recommended mixing volume, the resulting concentration (mg/mL), and exact insulin syringe units. Works for retatrutide, tirzepatide, semaglutide, BPC-157, and any injectable peptide.
Already added BAC water? Calculate concentration & syringe units.
For the “I already added water” flow, use the Peptide Units Converter and the BAC water helper to calculate concentration and syringe units.
Peptide concentration reference table
Resulting concentration (mg/mL) for common vial sizes and BAC water volumes.
| Vial size | + 1 mL BAC water | + 2 mL BAC water | + 2.5 mL BAC water | + 5 mL BAC water |
|---|---|---|---|---|
| 2 mg | 2.00 mg/mL | 1.00 mg/mL | 0.80 mg/mL | 0.40 mg/mL |
| 3 mg | 3.00 mg/mL | 1.50 mg/mL | 1.20 mg/mL | 0.60 mg/mL |
| 5 mg | 5.00 mg/mL | 2.50 mg/mL | 2.00 mg/mL | 1.00 mg/mL |
| 10 mg | 10.00 mg/mL | 5.00 mg/mL | 4.00 mg/mL | 2.00 mg/mL |
| 15 mg | 15.00 mg/mL | 7.50 mg/mL | 6.00 mg/mL | 3.00 mg/mL |
How peptide reconstitution with BAC water works
Most injectable peptides are supplied as lyophilized powder — freeze-dried peptide in a sealed vial. Before use, you reconstitute the powder by injecting bacteriostatic water (BAC water) through the rubber stopper. The BAC water dissolves the powder into a clear solution ready for injection.
The reconstitution → dosing flow
- 1Calculate concentration: Vial mg ÷ BAC water mL = mg/mL
- 2Calculate volume per dose: Dose mg ÷ concentration mg/mL = mL
- 3Convert to syringe units: Volume mL × 100 = units (U-100 syringe)
Why BAC water? Bacteriostatic water contains 0.9% benzyl alcohol, a preservative that inhibits bacterial growth. This extends the shelf life of your reconstituted peptide to approximately 28–30 days when refrigerated, making it suitable for multi-dose vials. Sterile water (without preservative) should only be used for single injections.
Storage tip: Once reconstituted, store peptide vials refrigerated at 2–8°C (35–46°F), protected from light. Do not freeze. Discard if the solution appears cloudy, discolored, or contains particulates.
How long does BAC water last? Storage & refrigeration
Two related questions come up constantly: how long does BAC water last and does BAC water need to be refrigerated? The answer depends on what you mean — the BAC water vial itself vs a peptide vial after reconstitution.
- BAC water (unopened): Follow the manufacturer’s label (expiration date, storage conditions).
- BAC water (after first puncture/opening): Many multi-dose bacteriostatic water products are commonly treated as usable for ~28 days after first puncture, but you should follow the vial label and your provider’s protocol.
- Does BAC water need to be refrigerated? Often it does not, but storage depends on the product label. In contrast, most reconstituted peptides should be refrigerated (typically 2–8°C / 35–46°F) and protected from light.
- How to store BAC water: Keep it clean, avoid touching needles to non-sterile surfaces, and discard if contamination is suspected (cloudiness, particulates, color change).
Always follow the specific storage and beyond-use guidance provided by your prescribing clinician or compounding pharmacy.
Frequently Asked Questions
How much bacteriostatic water should I add to my peptide vial?
How much BAC water for 10 mg retatrutide?
How much BAC water to mix with 30 mg tirzepatide?
What is bacteriostatic water and why is it used for peptides?
How do I calculate my peptide concentration after adding BAC water?
How does BAC water volume affect my syringe units per dose?
How long does reconstituted peptide last in the refrigerator?
What is the difference between this tool and the Peptide Reconstitution Calculator?
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Find a peptide-prescribing clinic
MyPeptideMatch connects you with licensed clinics that prescribe GLP-1 peptides and peptide therapy protocols. Providers supply all necessary reconstitution supplies and instructions.
Medical disclaimer: This tool is provided for informational and educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Peptide reconstitution and dosing should be supervised by a licensed healthcare provider. Always follow the specific reconstitution instructions provided by your prescribing physician or compounding pharmacy.