Peptide Reconstitution Calculator
To reconstitute a peptide vial, divide the vial strength in milligrams by the millilitres of bacteriostatic water you add. That gives the concentration in mg/mL. To find the syringe units for a given dose, divide the dose by the concentration to get the volume in millilitres, then multiply by 100 for a U-100 insulin syringe.
The formula
units = (dose mg ÷ (vial mg ÷ BAC water mL)) × 100
The inner division gives the concentration in mg per mL. Dividing the dose by that concentration gives the volume in millilitres. Multiplying by 100 converts millilitres to units on a U-100 insulin syringe, where 100 units equals 1 mL.
Calculate your dose
Enter your vial and dose to see the units to draw.
- Concentration
- 2.5 mg/mL
- Volume to draw
- 0.1 mL
- Per unit
- 25 mcg
- Doses per vial
- 20
Worked examples
Common vial and bacteriostatic water pairings, with the resulting concentration and units to draw.
5 mg vial, 2 mL water
10units
- Concentration
- 2.5 mg/mL
- Dose
- 0.25 mg
- Volume
- 0.1 mL
10 mg vial, 2 mL water
20units
- Concentration
- 5 mg/mL
- Dose
- 1 mg
- Volume
- 0.2 mL
15 mg vial, 3 mL water
50units
- Concentration
- 5 mg/mL
- Dose
- 2.5 mg
- Volume
- 0.5 mL
30 mg vial, 3 mL water
25units
- Concentration
- 10 mg/mL
- Dose
- 2.5 mg
- Volume
- 0.25 mL
Frequently asked questions
- How much bacteriostatic water do I add to a 10 mg vial?
- Any volume works arithmetically — it changes the concentration, not the total peptide in the vial. Adding 1 mL to a 10 mg vial gives 10 mg/mL, and 2 mL gives 5 mg/mL. More water means more syringe units for the same dose, which makes small doses easier to measure accurately. Your supplier's or prescriber's instructions take precedence.
- How many units is 0.25 mg?
- It depends entirely on the concentration. At 2.5 mg/mL (a 5 mg vial in 2 mL of water), 0.25 mg is 0.1 mL, which is 10 units on a U-100 syringe. At 5 mg/mL, the same 0.25 mg is only 5 units.
- What does U-100 mean on an insulin syringe?
- U-100 means the syringe is marked at 100 units per millilitre, so 100 units is 1 mL and 10 units is 0.1 mL. Units are a volume marking, not a measure of mass — the milligrams they represent depend on your concentration.
- Does adding more bacteriostatic water reduce the dose?
- No. It dilutes the peptide, so the same dose occupies a larger volume and more syringe units, but the milligrams delivered are unchanged if you draw the correct number of units.
- How do I reconstitute a 30 mg vial?
- Adding 3 mL of bacteriostatic water to a 30 mg vial gives 10 mg/mL. A 2.5 mg dose is then 0.25 mL, or 25 units on a U-100 syringe.
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