Bacteriostatic Water Calculator
Work backward from the draw you want. Enter your vial strength and dose, choose a target, and get the exact amount of bacteriostatic water to add, with the resulting draw on a to-scale insulin syringe.
Loading the bacteriostatic water calculator
Enter your vial strength and dose, pick a target draw in units or a target concentration, and see the exact volume of bacteriostatic water to add.
How to calculate bacteriostatic water
- 1Enter your vial strength. Type the total milligrams of peptide printed on the vial label.
- 2Enter your dose. Set the dose you plan to inject, in milligrams or micrograms.
- 3Pick your target. Choose the unit mark you want your dose to land on, or a target concentration in mg/mL.
- 4Read the water to add. See the exact volume of bacteriostatic water to add, the resulting concentration, and the draw on a to-scale syringe.
Common questions
- How much bacteriostatic water should I add to my peptide vial?
- It depends on the dose you want and how you prefer to read it on your syringe. Enter your vial strength and dose, pick a target draw in units (or a target concentration), and this calculator gives you the exact volume of bacteriostatic water to add. A common choice is to add enough water so your dose lands on an easy-to-read mark like 10 or 20 units.
- How do I know how many units to draw after reconstitution?
- Once water is added, the concentration is your vial strength divided by the water volume (mg/mL). The volume to draw is your dose divided by that concentration, and units on a U-100 insulin syringe are that volume in mL times 100. This tool shows the resulting draw on a to-scale syringe.
- Can I add more or less bacteriostatic water?
- Yes. More water makes a weaker solution and a larger, easier-to-read draw; less water makes a stronger solution and a smaller draw. The total amount of peptide stays the same, so only the volume you inject changes, not the dose.
- Does the amount of bacteriostatic water change my dose?
- No. Reconstitution only changes the concentration and therefore how many units you draw for the same dose. The milligrams of peptide you inject are unchanged. Always base your dose on mg, not on the volume.
- What is bacteriostatic water?
- Bacteriostatic water is sterile water containing a small amount of benzyl alcohol that inhibits bacterial growth, which makes it suitable for multi-dose vials. It is the standard diluent used to reconstitute lyophilized (freeze-dried) peptides.
- Which syringe should I use?
- A 0.3 mL (30-unit) insulin syringe gives the most precise reading for small draws, while larger doses may need a 0.5 mL or 1 mL syringe. This calculator warns you whenever the required draw exceeds the capacity of the syringe you select.
Already know your water volume and want the dose the other way around? Use the Dose & Reconstitution Calculator.
For educational and research purposes only. Not medical advice.
Related reading
- Reconstitution & mixing
How to Reconstitute a Peptide
To reconstitute a peptide, slowly add bacteriostatic water down the side of the vial, let it dissolve without shaking, then divide the vial strength by the water volume to get a mg/mL concentration. Divide your dose by that concentration to find the volume, and multiply by 100 for units on a U-100 syringe.
- Reconstitution & mixing
Bacteriostatic Water Explained
Bacteriostatic water is sterile water with about 0.9% benzyl alcohol added to inhibit bacterial growth, making it suitable for multi-dose vials. It is the standard diluent for reconstituting lyophilized peptides. The volume you add sets the concentration and how many units you draw, but never changes the milligram dose itself.