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Calculate exactly how much bacteriostatic water to add to your peptide vial to achieve your desired concentration. Includes shelf life and storage guidance.
How many mg is on the label?
Bacteriostatic water — not sure how much? Let the calculator pick.
How much per shot?
250 mcg = 0.25 mg
Pick the one in your hand.
Not sure? Look at the biggest number printed on the barrel — 30, 50 or 100.
Check the box says U-100. Syringes for pet insulin (U-40) look the same but their lines measure 2.5× more liquid. This calculator is for U-100 syringes only.
Each line on this syringe = 2 units = 50 mcg.
Easy check: 10 units = 250 mcg · 20 units = 500 mcg
Bacteriostatic water (BAC water) is sterile water that contains 0.9% benzyl alcohol as a bacteriostatic preservative. This preservative inhibits bacterial growth, making it the preferred solvent for reconstituting peptides that will be stored and used over multiple days.
BAC water contains a preservative (benzyl alcohol) that keeps the solution safe for up to 28 days when stored at 2-8°C. Sterile water does not contain a preservative, so reconstituted peptides should be used within 24-48 hours. For multi-dose vials, BAC water is strongly recommended.
The volume of bacteriostatic water you add does not change the total peptide in the vial - a 5 mg vial contains 5 mg of peptide regardless of whether you add 1 mL or 5 mL of water. What changes is the concentration, which determines how much liquid you draw per dose.
| BAC Water Added | Concentration | Draw per 250 mcg Dose | Draw per 500 mcg Dose |
|---|---|---|---|
| 1.0 mL | 5.0 mg/mL | 5 units | 10 units |
| 2.0 mL | 2.5 mg/mL | 10 units | 20 units |
| 3.0 mL | 1.67 mg/mL | 15 units | 30 units |
| 5.0 mL | 1.0 mg/mL | 25 units | 50 units |
Based on a 5 mg vial using a U-100 insulin syringe (100 units = 1 mL).
Adding too little water creates a high concentration where each dose requires only a few syringe units - 2 or 3 units is nearly impossible to measure accurately, and a 1-unit error represents a 30-50% dosing error. Adding too much water creates a low concentration where each dose requires a large draw volume - potentially exceeding the syringe capacity.
Adding less than 0.5 mL of BAC water to a standard 5-10 mg vial creates a concentration where each dose requires under 5 syringe units. At these volumes, a 1-unit measurement error represents 20-50% of the intended dose, resulting in wildly inconsistent dosing from injection to injection.
The fix: Use the minimum BAC water volume that places your dose draw at 5+ units on your syringe. If the dose is inherently small (under 100 mcg), switch to a 30-unit (0.3 mL) syringe for finer graduation marks.
Adding 5+ mL of BAC water to a 5 mg vial creates a concentration of 1 mg/mL or less. At common dose ranges (250-500 mcg), this produces draw volumes of 25-50 units - approaching the full capacity of a 50-unit syringe and creating larger, more uncomfortable injections.
The fix: Use the calculator to find the BAC water volume that keeps your draw in the 5-20 unit range. For a full breakdown of reconstituted peptide stability, see how to store peptides.
| Peptide | Vial Size | Typical Dose | Common BAC Water | Concentration | Draw per Dose |
|---|---|---|---|---|---|
| BPC-157 | 5 mg | 250 mcg | 2 mL | 2.5 mg/mL | 10 units |
| BPC-157 | 10 mg | 500 mcg | 2 mL | 5.0 mg/mL | 10 units |
| TB-500 | 5 mg | 2.5 mg | 1 mL | 5.0 mg/mL | 50 units |
| Ipamorelin | 5 mg | 200 mcg | 2 mL | 2.5 mg/mL | 8 units |
| CJC-1295 no DAC | 5 mg | 100 mcg | 2 mL | 2.5 mg/mL | 4 units |
| Semaglutide | 3 mg | 250 mcg | 1 mL | 3.0 mg/mL | 8 units |
| Semaglutide | 5 mg | 1 mg | 1 mL | 5.0 mg/mL | 20 units |
| Tirzepatide | 10 mg | 2.5 mg | 2 mL | 5.0 mg/mL | 50 units |
| Tirzepatide | 30 mg | 5 mg | 3 mL | 10.0 mg/mL | 50 units |
| Retatrutide | 12 mg | 2 mg | 2 mL | 6.0 mg/mL | 33 units |
| Sermorelin | 5 mg | 200 mcg | 2 mL | 2.5 mg/mL | 8 units |
| GHK-Cu | 50 mg | 1 mg | 5 mL | 10.0 mg/mL | 10 units |
| Selank | 5 mg | 250 mcg | 2 mL | 2.5 mg/mL | 10 units |
| Semax | 5 mg | 200 mcg | 2 mL | 2.5 mg/mL | 8 units |
| PT-141 | 10 mg | 1 mg | 2 mL | 5.0 mg/mL | 20 units |
| Melanotan II | 10 mg | 500 mcg | 2 mL | 5.0 mg/mL | 10 units |
It depends on your dose. For 250 mcg, adding 2 mL creates a 2.5 mg/mL concentration where each dose draws 10 units. For 500 mcg, 1 mL produces 5.0 mg/mL at 10 units per dose. Use the calculator above with your specific dose.
Yes - adding more BAC water further dilutes the concentration. The peptide is not harmed. Update the total BAC water volume in the reconstitution calculator to recalculate your new draw volume. The 28-day stability clock starts from the first reconstitution, not from when you add more water.
Sterile water contains no preservative. Reconstituted peptides in sterile water should be used within a single session or discarded - each needle insertion introduces potential contamination with no antimicrobial protection. For multi-dose vials, bacteriostatic water is required.
No. A 5 mg vial contains 5 mg of peptide regardless of how much water you add. The water changes the concentration (mg/mL), which changes how much liquid you draw - but the actual peptide content per draw remains whatever dose you calculate.
Unopened BAC water has a shelf life of 12-24 months (per manufacturer). Once the stopper is punctured, use the remaining water within 28 days and store at room temperature or refrigerated. Discard if cloudy or discolored.
A 100-unit (1 mL) U-100 insulin syringe is standard. For very small doses (under 10 units), a 30-unit (0.3 mL) syringe provides finer graduation marks - each tick is 0.5 units instead of 1 - improving measurement accuracy.