When a peptide vial is reconstituted, the powder dissolves into BAC water to create a solution with a known concentration. Injection volume is calculated by dividing the target dose by the concentration. The result is then converted to syringe units for use with a U-100 insulin syringe.
Worked example: 5 mg vial + 2 mL BAC water. Step 1: 5 mg x 1,000 = 5,000 mcg. Step 2: 5,000 / 2 = 2,500 mcg/mL. Step 3: 250 mcg dose / 2,500 mcg/mL = 0.1 mL. Step 4: 0.1 mL x 100 = 10 units on a U-100 syringe. Doses per vial: 5,000 / 250 = 20 doses.
This calculation pattern, dividing a total amount by a concentration to get a required volume, appears in other clinical math. The Corrected Calcium Calculator uses a similar correction factor approach to adjust a measured value based on a concentration variable (albumin).
The volume of BAC water you add to a vial directly controls the concentration and the injection volume per dose. More water means a more dilute solution and a larger injection volume; less water means higher concentration and a smaller injection volume. The table below shows how water volume affects units per dose for a 5 mg vial.
| BAC Water (5 mg vial) | Concentration | 250 mcg dose | 500 mcg dose |
|---|---|---|---|
| 1 mL | 5,000 mcg/mL | 5 units (0.05 mL) | 10 units (0.10 mL) |
| 2 mL | 2,500 mcg/mL | 10 units (0.10 mL) | 20 units (0.20 mL) |
| 3 mL | 1,667 mcg/mL | 15 units (0.15 mL) | 30 units (0.30 mL) |
| 5 mL | 1,000 mcg/mL | 25 units (0.25 mL) | 50 units (0.50 mL) |
Practical guideline: Use 2 mL BAC water as the default for most 5 mg peptide vials. This gives 2,500 mcg/mL, and common research doses (100 to 500 mcg) fall in the comfortable 4 to 20 unit range. For very small doses (under 100 mcg), add more water to spread the dose across a larger injection volume for more accurate measurement. For a second clinical lab calculation built around the same concentration math, see the Anion Gap Calculator.
The table below shows research dose ranges, typical vial sizes, suggested BAC water volumes, and the resulting syringe units for the most frequently researched peptides. All values assume a U-100 insulin syringe and 2 mL BAC water per vial unless otherwise noted.
| Peptide | Common Dose | Vial Size | BAC Water | Syringe Units |
|---|---|---|---|---|
| BPC-157 | 250 mcg | 5 mg | 2 mL | 10 units |
| TB-500 | 2,000 mcg | 5 mg | 2 mL | 80 units |
| CJC-1295 (no DAC) | 100 mcg | 2 mg | 2 mL | 10 units |
| Ipamorelin | 200 mcg | 2 mg | 2 mL | 20 units |
| Sermorelin | 300 mcg | 3 mg | 2 mL | 20 units |
| PT-141 (Bremelanotide) | 1,000 mcg | 10 mg | 2 mL | 20 units |
| Epithalon | 5,000 mcg | 10 mg | 2 mL | 100 units |
GLP-1 receptor agonists such as tirzepatide and semaglutide are increasingly researched in peptide form for metabolic applications. These peptides are typically prescribed in milligram doses per week, not micrograms, and their dosing follows different titration protocols than research peptides. For metabolic health monitoring alongside GLP-1 research, the A1C Calculator provides context on long-term blood glucose control.
A researcher reconstitutes a 10 mg BPC-157 vial with 4 mL BAC water and wants a 500 mcg dose.
20 units on the syringe barrel equals 0.2 mL. The 10 mg vial provides 20 doses at this dose size. Using 4 mL of BAC water (vs 2 mL) halves the concentration but doubles the injection volume, keeping the 500 mcg dose in a comfortable 20-unit range instead of 10 units with a more concentrated mix.