Bacteriostatic water calculator
Bacteriostatic water (sterile water with 0.9% benzyl alcohol) is the diluent used to reconstitute lyophilised research peptides. How much you add sets the concentration: less water = more concentrated (fewer units per dose), more water = more dilute (more units per dose, easier to measure small amounts).
Units to draw
10units
- Concentration
- 2.5 mg/mL
- per unit
- 25 mcg
- Volume per dose
- 0.1 mL
- Doses per vial
- ~2
How much bacteriostatic water should you add?
There is no single correct amount — it's a trade-off. Most references use 1–3 mL per vial. More water makes small doses easier to measure precisely on the syringe; less water keeps the total injection volume low. Enter your vial size and target dose above to see the resulting concentration and units for any water volume.
The math
Concentration (mg/mL) = vial mg ÷ water mL. Units to draw = (dose in mcg ÷ (concentration × 1000)) × 100 on a U-100 syringe.
Worked examples
Verified reference figures for common vial sizes on a U-100 (insulin) syringe. These are unit-conversion results, not dose recommendations.
| Peptide in vial | Bacteriostatic water | Dose | Concentration | Volume | Units to draw |
|---|---|---|---|---|---|
| 5 mg | 2 mL | 250 mcg | 2.5 mg/mL | 0.10 mL | 10 units |
| 10 mg | 2 mL | 500 mcg | 5 mg/mL | 0.10 mL | 10 units |
| 5 mg | 1 mL | 250 mcg | 5 mg/mL | 0.05 mL | 5 units |
| 2 mg | 1 mL | 100 mcg | 2 mg/mL | 0.05 mL | 5 units |
Frequently asked questions
How do I calculate peptide reconstitution?
Divide the milligrams of peptide in the vial by the millilitres of bacteriostatic water to get the concentration in mg/mL. To find the units to draw on a U-100 syringe, divide your dose in mcg by the concentration in mcg/mL (concentration × 1000), then multiply by 100. For example, 5 mg in 2 mL gives 2.5 mg/mL; a 250 mcg dose is 0.10 mL, or 10 units.
How many units is one dose on an insulin syringe?
On a U-100 syringe, 100 units equals 1 mL. So 10 units is 0.10 mL and 50 units is 0.50 mL. The exact number of units for a given dose depends on the concentration you reconstituted to — use the calculator above to convert.
Does adding more water make the peptide weaker?
No. The total amount of peptide stays the same; adding more water only lowers the concentration. You then draw a larger volume (more units) to deliver the same amount of peptide. More water can make small amounts easier to measure accurately.
What water is used to reconstitute peptides?
Bacteriostatic water — sterile water containing 0.9% benzyl alcohol, which inhibits bacterial growth and allows multiple withdrawals over time. This is a laboratory handling note for research-use-only material, not human-use guidance.
Is this calculator medical advice?
No. It performs unit-conversion arithmetic only (mg, mL, mcg, syringe units). It is not medical, dosing or treatment advice. Research peptides are not approved for human or veterinary use.