Peptide reconstitution calculator
Enter the mg in your vial and the bacteriostatic water you added to get the resulting concentration in mg/mL. This calculates concentration only — it does not tell you what dose to take or how many units to draw. Always confirm your dose with a licensed prescriber or pharmacist.
Inputs
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Result
Live-computed.
Concentration once mixed
5.00 mg/mL
Reference only — not medical advice and not a dosing recommendation. This tool does not calculate how much to draw or inject. Ask your prescriber or pharmacist how many units to draw.
Want to see it on a syringe? Try the visual dose calculator.
How to use this calculator
Enter the mg per vial — typically printed on the vial label (e.g. 5 mg or 10 mg) — and how many milliliters of bacteriostatic water you mixed in. The calculator shows the resulting concentration. It does not accept a dose or output syringe units; how much to draw is a question for your prescriber or pharmacist.
The reconstitution formula
Reconstitution maths is one division. The peptide dissolves evenly through whatever water you add, so:
Concentration (mg/mL) = mg in the vial ÷ mL of BAC water addedConcentration (mcg/mL) = (mg in the vial × 1000) ÷ mL of BAC water added
Adding more BAC water does not change how much peptide is in the vial — it only spreads the same amount through more liquid. That is why dilution changes the volume you draw, never the total drug available.
Concentration by vial size and BAC water
Every value below is the vial size divided by the water added. Find your vial in the left column and your water volume across the top.
| Vial size | 1 mL | 2 mL | 3 mL | 5 mL |
|---|---|---|---|---|
| 5 mg | 5 mg/mL | 2.5 mg/mL | 1.67 mg/mL | 1 mg/mL |
| 10 mg | 10 mg/mL | 5 mg/mL | 3.33 mg/mL | 2 mg/mL |
| 15 mg | 15 mg/mL | 7.5 mg/mL | 5 mg/mL | 3 mg/mL |
| 30 mg | 30 mg/mL | 15 mg/mL | 10 mg/mL | 6 mg/mL |
Higher concentration means a smaller injection volume, but less margin for measurement error on small doses.
How to reconstitute a peptide vial
- Let the lyophilised vial and the bacteriostatic water reach room temperature before you start.
- Wipe the rubber stopper on both vials with a fresh 70% alcohol swab and let them air dry.
- Draw your measured volume of bacteriostatic water into the syringe.
- Angle the needle so the water runs down the inside glass wall of the peptide vial — never spray it directly onto the powder.
- Swirl or roll the vial gently until the solution is completely clear. Never shake it; agitation degrades the peptide.
- Label the vial with the concentration and the date you mixed it, then store it as the manufacturer directs.
Concentration explained
Concentration is simply mg ÷ mL. A vial with 10 mg of peptide reconstituted with 2 mL of BAC water yields 5 mg/mL. Higher concentrations mean smaller injection volumes but less margin for measurement error.
Common pitfalls
- Using regular sterile water instead of bacteriostatic water for multi-use vials.
- Reconstituting with too little BAC water → concentration too high → tiny doses become imprecise.
- Shaking the vial to speed dissolution instead of swirling it gently.
- Spraying water directly onto the lyophilised powder rather than down the vial wall.
- Forgetting that your stored, reconstituted vial has a limited shelf life.
FAQ
- What is peptide reconstitution?
- Reconstitution is the process of mixing a lyophilized (freeze-dried) peptide with bacteriostatic water to create an injectable solution at a known concentration.
- How do I calculate peptide reconstitution?
- Divide the milligrams in the vial by the millilitres of bacteriostatic water you added. A 10 mg vial with 2 mL of water gives 10 ÷ 2 = 5 mg/mL. To express it in micrograms per millilitre, multiply the milligrams by 1000 first.
- How much bacteriostatic water should I add to a 5 mg vial?
- There is no single correct volume — it depends on the concentration you and your prescriber are aiming for. 1 mL gives 5 mg/mL, 2 mL gives 2.5 mg/mL and 5 mL gives 1 mg/mL. More water makes small doses easier to measure accurately; less water keeps the injection volume small.
- Does adding more BAC water change my dose?
- It changes the volume you draw, not the amount of peptide in the vial. Doubling the water halves the concentration, so you would draw twice the volume for the same amount of peptide. The total drug in the vial is unchanged.
- Does this calculator tell me how many units to draw?
- No. It converts mg per vial and BAC water into a concentration (mg/mL) for your reference. It does not calculate a dose or how many units to draw or inject — ask your prescriber or pharmacist.
- Why not just tell me the units?
- Dosing decisions depend on factors this tool can’t see. We keep this strictly a concentration calculator so you always confirm the actual draw amount with a licensed professional.
- What is the difference between bacteriostatic and sterile water?
- Bacteriostatic water contains 0.9% benzyl alcohol, which suppresses bacterial growth and allows a vial to be entered more than once. Plain sterile water has no preservative and is intended for single use.
- Can I use this for GLP-1 medications like semaglutide or tirzepatide?
- The concentration maths is identical for any lyophilised compound. We also publish dedicated calculators for semaglutide and tirzepatide with typical vial sizes pre-filled.
This page is for informational purposes only and is not medical advice. Always verify dosing with a licensed clinician.
By vial size
Worked mixing charts for a specific vial strength — water volumes, concentration, and the units each dose reads.