BAC Water Calculator
Enter your vial size and target dose. The calculator recommends how much bacteriostatic water to add so your syringe draws are precise and practical.
How many milligrams are in your peptide vial?
What dose do you want per injection?
Select your vial size and dose above to get a water recommendation.
How BAC water reconstitution works
The water volume is the one variable you control. It does not change your dose. It changes how easy that dose is to measure.
Powder meets water
Your peptide arrives as lyophilized (freeze-dried) powder. Adding BAC water dissolves it into an injectable solution. The amount of water you choose sets the concentration.
Concentration determines draw volume
Less water = higher concentration = fewer syringe units per dose. More water = lower concentration = more units per dose. Neither changes the actual dose in micrograms.
Precision is the goal
You want your dose to land in a range that is easy to measure on your syringe. Drawing 2 units is hard to read accurately. Drawing 10-20 units is straightforward. This calculator finds the water volume that hits that sweet spot.
Worked examples
Four common reconstitutions across the peptide catalog, with every step traced through to the syringe unit you would actually draw.
5 mg BPC-157 vial, 250 mcg target dose
Reconstituting with 2 mL of BAC water gives a 2.5 mg/mL concentration. A 250 mcg dose equals 0.1 mL, which reads as 10 units on a U-100 insulin syringe. That sits squarely in the 10 to 20 unit readability sweet spot. The vial yields roughly 20 doses across the 28 day refrigerated window.
10 mg tirzepatide vial, 5 mg weekly dose
Reconstituting with 2 mL of BAC water gives a 5 mg/mL concentration. A 5 mg weekly dose equals 1 mL, which is 100 units on a standard U-100 syringe. That fills the barrel completely. For lower titration doses (2.5 mg), the same vial gives 0.5 mL or 50 units, easier to draw with room to spare.
2 mg ipamorelin vial, 200 mcg dose
Reconstituting with 2 mL of BAC water gives a 1 mg/mL concentration. A 200 mcg dose equals 0.2 mL, which is 20 units on the syringe. Drawing 20 units gives generous tick-mark spacing and is easy to read in low light, which matters for evening protocols where many GH-axis peptides are dosed before sleep.
5 mg semaglutide vial, 0.25 mg starting dose
Reconstituting with 2 mL of BAC water gives a 2.5 mg/mL concentration. A 0.25 mg starting dose equals 0.1 mL, which is 10 units. That works for week 1 to week 4 of the standard titration. As the dose escalates to 0.5 mg then 1.0 mg, the draw scales to 20 then 40 units, all well within syringe range, so the same vial setup carries through the first three titration steps.
Common reconstitution mistakes
The four patterns most responsible for dosing errors in self-administered peptide protocols.
Confusing milliliters with syringe units
A standard U-100 insulin syringe has 100 units per 1 mL. A 50 unit draw is half a mL, not 50 mL. The most common dosing error is reading 50 on the barrel and thinking it means 50 mg. Always convert through concentration before drawing.
Drawing too close to the bottom of the vial
Tilt the vial gently rather than pulling the needle through the stopper to the absolute bottom. Stopper-bound rubber particulate can detach and end up in the syringe. A 45 degree tilt with the needle bevel down lets you draw cleanly without stopper contact at the bottom.
Using BAC water past the 28 day puncture window
The 28 day rule starts from first puncture, not first opening. Mark the puncture date on the vial label with a marker. After 28 days the benzyl alcohol preservative weakens and reconstituted peptide stability is no longer reliable.
Picking a water volume that produces single-digit unit draws
If your target dose works out to 3 or 4 units on the syringe, you have effectively no precision floor. A 1 unit error becomes a 25 to 33 percent dose deviation. Reconstitute with a larger water volume so the same dose lands at 10 units or more, where a 1 unit error is a 10 percent deviation at most.
BAC water shelf life and storage
The benzyl alcohol in BAC water is what makes multi-dose vials possible. Without it, you would need to use the entire vial in a single session.
Unopened BAC water
Room temperature is fine. Check the expiration date on the vial. Most manufacturers give it 2-3 years from production.
After reconstitution
Refrigerate at 2-8 degrees C. Stable for approximately 28 days. Keep the vial upright, protected from light. Discard after 30 days regardless of remaining volume.
Sterile water is the exception. It has no preservative, so reconstituted peptides must be used within 24 hours. Only use sterile water if you plan to use the full vial in one session.
Concentration reference
Quick lookup for resulting concentration (mg/ml) based on your vial size and water volume. Higher concentration means fewer units per dose.
| Vial | 1 ml | 2 ml | 2.5 ml | 5 ml |
|---|---|---|---|---|
| 2 mg | 2.00 | 1.00 | 0.80 | 0.40 |
| 3 mg | 3.00 | 1.50 | 1.20 | 0.60 |
| 5 mg | 5.00 | 2.50 | 2.00 | 1.00 |
| 10 mg | 10.00 | 5.00 | 4.00 | 2.00 |
| 15 mg | 15.00 | 7.50 | 6.00 | 3.00 |
All values in mg/ml. To convert your dose: units = (dose in mcg) / (concentration x 1,000) x 100.
Common questions
BAC water volume, storage, and how it relates to your dose.
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