Peptide Reconstitution Calculator
Calculate the exact number of syringe units to draw for any peptide dose after reconstituting with bacteriostatic water.
mg
mL
Draw This Amount
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insulin syringe units
Concentration
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mcg per unit
Doses Per Vial
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full doses
Suggested BAC Water Amounts for Round Syringe Marks
| BAC Water | Units Per Dose | Concentration | Doses Per Vial |
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Create Free AccountHow to Reconstitute Peptides
Reconstitution is the process of adding bacteriostatic water (BAC water) to a freeze-dried peptide powder to create an injectable solution. Here's how to do it safely and accurately.
What You'll Need
- Your peptide vial — containing lyophilized (freeze-dried) powder
- Bacteriostatic water — sterile water with 0.9% benzyl alcohol as a preservative
- Insulin syringes — standard U-100 (100 units = 1 mL)
- Alcohol swabs — for sterilizing vial tops
Step-by-Step Process
- Determine how much BAC water to add. Use the calculator above. The amount depends on your vial size and desired dose. Aim for a volume that gives you a round number of syringe units per dose (like 10, 20, 25, or 50 units).
- Clean the vial tops. Swab both the peptide vial and the BAC water vial with alcohol pads.
- Draw the BAC water. Using an insulin syringe, draw the calculated amount of bacteriostatic water.
- Add water slowly. Insert the needle into the peptide vial at an angle and let the water run down the side of the glass. Do not spray directly onto the powder — this can damage the peptide.
- Gently swirl. Once the water is added, gently swirl the vial until the powder is fully dissolved. Do not shake vigorously.
- Store properly. Refrigerate the reconstituted vial at 2–8°C. Most reconstituted peptides are stable for 28–30 days.
Understanding the Math
A standard insulin syringe has 100 units per 1 mL. When you add BAC water to a peptide vial, you create a solution with a known concentration:
Concentration (mcg/unit) = (Peptide mg × 1000) ÷ (BAC water mL × 100)
For example: 5 mg of BPC-157 in 2 mL of BAC water = (5 × 1000) ÷ (2 × 100) = 25 mcg per unit. To get a 250 mcg dose, you'd draw 10 units.
Common Questions
How much bacteriostatic water should I add to my peptide vial?
The amount of BAC water depends on the peptide amount in the vial and the concentration you want. A common approach is to add enough water so your typical dose falls on a round syringe mark. For example, with a 5mg BPC-157 vial and a 250mcg dose, adding 2mL of BAC water gives you 25 units per dose. Use the "Suggested BAC Water Amounts" table above to find the best volume for your setup.
What's the difference between bacteriostatic water and sterile water?
Bacteriostatic water contains 0.9% benzyl alcohol, which inhibits bacterial growth. This means you can withdraw from the same vial multiple times over days or weeks. Sterile water has no preservative and should only be used once. For peptides that you'll dose from repeatedly, always use bacteriostatic water.
Can I use this calculator for semaglutide and tirzepatide?
Yes. Select semaglutide or tirzepatide from the dropdown and choose your vial size. The math works the same for all injectable peptides. Note that GLP-1 peptides like semaglutide often come in larger vial sizes (3mg, 5mg, 10mg) and are dosed weekly rather than daily.
How many doses are in one vial?
Divide the total peptide amount (in mcg) by your dose (in mcg). For example, a 5mg vial at 250mcg per dose gives you 20 doses (5000 ÷ 250 = 20). The calculator shows this automatically in the "Doses Per Vial" box.
How long does reconstituted peptide last?
Most reconstituted peptides last 28–30 days when stored in the refrigerator at 2–8°C. Some peptides like semaglutide may last longer due to their stability. Never freeze reconstituted peptides, and never leave them at room temperature for extended periods. Always store with the cap on to protect from light.
What size syringe should I use?
Most people use U-100 insulin syringes (100 units = 1 mL). Common needle sizes are 29-31 gauge with 1/2 inch length for subcutaneous injections. If your dose is under 30 units, a 0.3mL (30 unit) syringe gives finer markings and more accurate measurement. For larger doses, use a standard 1mL (100 unit) syringe.