Reconstitution tool
BAC Water Calculator: Pick the Right Mix Volume
By Baris Bingor · Last updated
How much bacteriostatic water should I add?
The water doesn't change how much peptide is in the vial; it sets the concentration, and so how many units an amount fills. In a 5 mg vial, 250 mcg is 5 units with 1 mL of water, 10 units with 2 mL and 25 units with 5 mL. A common choice is a volume that puts the amount between 10 and 50 units, which is easy to read on a U-100 syringe.
Reconstitution calculator
Type your own numbers. They aren't sent anywhere: the math runs in your browser.
Type an amount to see the volume and the units.
Arithmetic only. Peptly does not suggest amounts: the amount is yours, from your protocol or the product's documentation. Not medical advice.
The formula
- Concentration (mg/mL) = peptide in the vial (mg) ÷ water added (mL).
- Volume to draw (mL) = amount (mg) ÷ concentration (mg/mL). 1 mg = 1,000 mcg.
- U-100 units = volume (mL) × 100. On a U-100 insulin syringe, 1 unit = 0.01 mL and 100 units = 1 mL.
Worked examples
- 5 mg vial, 1 mL water, 250 mcg: 5 mg ÷ 1 mL = 5 mg/mL. 250 mcg (0.25 mg) ÷ 5 mg/mL = 0.05 mL. 0.05 mL × 100 = 5 units on a U-100 syringe.
- 5 mg vial, 2 mL water, 250 mcg: 5 mg ÷ 2 mL = 2.5 mg/mL. 250 mcg (0.25 mg) ÷ 2.5 mg/mL = 0.1 mL. 0.1 mL × 100 = 10 units on a U-100 syringe.
- 5 mg vial, 5 mL water, 250 mcg: 5 mg ÷ 5 mL = 1 mg/mL. 250 mcg (0.25 mg) ÷ 1 mg/mL = 0.25 mL. 0.25 mL × 100 = 25 units on a U-100 syringe.
- 10 mg vial, 3 mL water, 500 mcg: 10 mg ÷ 3 mL = 3.333 mg/mL. 500 mcg (0.5 mg) ÷ 3.333 mg/mL = 0.15 mL. 0.15 mL × 100 = 15 units on a U-100 syringe.
| Water | mg/mL | 100 mcg | 250 mcg | 500 mcg | 1 mg |
|---|---|---|---|---|---|
| 1 mL | 5 | 2 | 5 | 10 | 20 |
| 2 mL | 2.5 | 4 | 10 | 20 | 40 |
| 3 mL | 1.667 | 6 | 15 | 30 | 60 |
| 4 mL | 1.25 | 8 | 20 | 40 | 80 |
| 5 mL | 1 | 10 | 25 | 50 | 100 |
| Water | mg/mL | 100 mcg | 250 mcg | 500 mcg | 1 mg |
|---|---|---|---|---|---|
| 1 mL | 10 | 1 | 2.5 | 5 | 10 |
| 2 mL | 5 | 2 | 5 | 10 | 20 |
| 3 mL | 3.333 | 3 | 7.5 | 15 | 30 |
| 4 mL | 2.5 | 4 | 10 | 20 | 40 |
| 5 mL | 2 | 5 | 12.5 | 25 | 50 |
Each cell is units on a U-100 syringe: amount ÷ (vial mg ÷ water mL) × 100. † More than one full 1 mL (100-unit) syringe. The amounts are columns of arithmetic, not suggestions; the amount is yours, from your protocol or the product's documentation. Not medical advice.
How to use the calculator to pick
Type the vial mass and your amount first, then try different water volumes until the unit count lands in a range you can read without squinting. Write the choice on the vial label so you do not re-derive it on every draw.
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
- Sterile vs bacteriostatic water — what's the difference
- Peptide calculator
- Reconstitution math reference
- Step-by-step reconstitution guide
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. The calculator on this page shows the unit count for any combination as you type.
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.