Last updated: May 2026
Peptide Reconstitution Calculator
About this calculator
The peptide reconstitution calculator answers one question: how much bacteriostatic water do I add to my vial? Enter your vial size (in mg or mcg) and your target concentration (mcg/mL) — the calculator gives you the exact BAC water volume using the formula BAC water (mL) = vial content (mg × 1000) ÷ target concentration (mcg/mL). Once you have your answer, hit Transfer to pre-fill the Peptide Dosage Calculator with your concentration and calculate per-injection draw volumes. Free, instant, no login.
How to use this calculator
You need two things: the amount of peptide in the vial (printed on the label — e.g., 10 mg) and the concentration you want to achieve in mcg/mL.
Enter the vial size first. If your vial is labelled in mcg instead of mg, tap the unit toggle to switch. Then set your target concentration — 1000 mcg/mL is a common starting point. The calculator instantly shows how many millilitres of BAC water to draw up and inject into the vial.
Once reconstituted, tap Transfer to Dosage Calculator to carry your concentration through to the dosage calculator and compute how many units to draw per injection.
Worked example — 10 mg vial at 1000 mcg/mL
Reconstitution
Vial size: 10 mg (10,000 mcg)
Target concentration: 1,000 mcg/mL
BAC water to add = 10,000 ÷ 1,000 = 10 mL
Worked example — 5 mg vial at 500 mcg/mL
Vial size: 5 mg (5,000 mcg)
Target concentration: 500 mcg/mL
BAC water to add = 5,000 ÷ 500 = 10 mL
Common reconstitution volumes by vial size
| Vial size | Target conc. | BAC water to add |
|---|
| 5 mg | 500 mcg/mL | 10 mL |
| 5 mg | 1,000 mcg/mL | 5 mL |
| 10 mg | 1,000 mcg/mL | 10 mL |
| 10 mg | 2,000 mcg/mL | 5 mL |
| 2 mg | 500 mcg/mL | 4 mL |
How to add BAC water to a peptide vial
Draw up the calculated BAC water volume into a sterile syringe. Insert the needle into the vial through the rubber stopper and let the water run slowly down the inside wall of the vial — do not aim directly at the powder. Once all the water is in, gently swirl (do not shake). The powder should dissolve completely within a minute. If it does not, let the vial sit refrigerated for 15–30 minutes and swirl again.
Store reconstituted vials refrigerated at 2–8°C and discard after 30 days, or per the manufacturer's guidance for your specific peptide.
Frequently asked questions
Does it matter how much BAC water I add?
Yes — the amount determines concentration, which directly changes how many units you draw per dose. Less BAC water = higher concentration = smaller injection volumes. More BAC water = lower concentration = larger injection volumes. There is no universally correct amount; it depends on your dose range and syringe preference.
What is bacteriostatic water?
Bacteriostatic water is sterile water preserved with 0.9% benzyl alcohol, which inhibits bacterial growth. It is the standard diluent for multi-dose peptide vials because the preservative keeps the reconstituted solution safe across multiple needle punctures. Do not use plain sterile water for multi-dose vials — it has no preservative.
What target concentration should I use?
1000 mcg/mL (1 mg/mL) is a common starting point because the maths is simple and the resulting injection volumes are manageable on a standard 1 mL insulin syringe. Higher concentrations mean smaller injections; lower concentrations mean larger ones. The right choice depends on your dose and syringe size.
Can I use sterile water instead of bacteriostatic water?
Sterile water has no preservative and is only suitable for single-use reconstitution. Bacteriostatic water is preferred for multi-dose vials. If your vial will be used in a single injection, sterile water is acceptable, but BAC water is the safer default for any multi-dose use.
How long does reconstituted peptide last?
Most peptides are stable for approximately 30 days when refrigerated at 2–8°C after reconstitution with bacteriostatic water. Stability varies by peptide — some are more fragile. Freeze lyophilised (unreconstituted) vials for long-term storage; once reconstituted, refrigerate and use within 30 days.
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