How much bacteriostatic water should I add to a 5 mg peptide vial?

Adding 2.0 mL of bacteriostatic water to a 5 mg vial creates a concentration of 2.5 mg/mL (25 mcg per syringe unit). At this concentration, a 0.25 mg starting dose is exactly 10 units on a standard U-100 syringe. If you add 1.0 mL instead, your concentration is 5.0 mg/mL and a 0.25 mg dose is 5 units.

What is the formula to calculate syringe units for reconstituted peptides?

The universal formula is: Syringe Units = (Prescribed Dose in mg / Vial Concentration in mg/mL) * 100. To find your vial concentration, divide the total peptide mg in the vial by the mL of bacteriostatic water added.

Can you shake a peptide vial after adding bacteriostatic water?

No. Never shake peptide vials. Shaking causes foaming, shearing, and denaturation of the fragile peptide amino acid chains. Instead, inject the liquid slowly down the inside glass wall and gently roll or swirl the vial between your fingers until fully dissolved.

How long is reconstituted peptide good for in the refrigerator?

Once reconstituted with bacteriostatic water containing 0.9% benzyl alcohol, vials should be stored between 36°F and 46°F (2°C–8°C) and used within 28 to 30 days. Protect from direct heat and light.

What syringe should I use for reconstituted peptides?

Standard U-100 insulin syringes with attached 31-gauge, 5/16-inch (8mm) needles are the industry standard for subcutaneous peptide injections. 100 units on a U-100 syringe equals exactly 1.0 mL.

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Peptide Reconstitution Calculator

Calculate bacteriostatic water volume, vial concentration (mg/mL), and exact U-100 syringe units for semaglutide, tirzepatide, and research peptides. 100% free.

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Clinical & Research Use Notice. This calculator performs arithmetic based on the numbers you enter. It does not provide medical advice or instructions to take unprescribed substances. If you are prescribed a compounded medication, always confirm the concentration and syringe dose printed on your prescription label before administration.

1. Vial & Liquid Inputs

Vial Peptide Quantity (mg)

Total powder in the vial (e.g., 5 mg, 10 mg, 15 mg).

5 mg 10 mg 15 mg 30 mg 50 mg

Bacteriostatic Water Added (mL)

Liquid volume added to reconstitute the powder.

1 mL 2 mL 2.5 mL 3 mL 5 mL

2. Desired Single Dose

Prescribed / Desired Dose

Common starting dose: 0.25 mg (250 mcg).

0.25 mg 0.5 mg 1.0 mg 1.7 mg 2.5 mg

Syringe Type

Standard insulin syringes are calibrated in U-100 (100 units = 1 mL).

Draw On Your Syringe:

10 Units

Equal to 0.10 mL of reconstituted liquid

Vial Summary & Concentration

Resulting Concentration	2.50 mg/mL (25 mcg per Unit)
Total Doses in This Vial	20 full doses of 0.25 mg
Liquid Volume per Dose	0.10 mL (10% of a 1 mL syringe)
Syringe Barrel Fill Gauge	10 / 100 units filled

Universal Reconstitution Protocol

To preserve peptide integrity and ensure absolute sterility, follow the standard laboratory protocol when adding bacteriostatic water:

Sanitize Both Vials: Wipe the rubber septums of both the bacteriostatic water vial and the peptide vial with fresh 70% isopropyl alcohol swabs. Allow to air dry for 10 seconds.
Equalize Air Pressure: Draw the exact volume of air into your syringe as the bacteriostatic water you plan to pull (e.g., 2 mL air for 2 mL water). Inject the air into the BAC water vial to maintain neutral pressure, then draw the water.
Angled Slow Injection: Insert the needle into the peptide vial angled against the inside glass wall. Slowly dispense the water down the wall rather than blasting directly onto the lyophilized powder, which can shear delicate amino acid chains.
Gentle Swirl (Never Shake): Gently swirl or roll the vial between your palms until the powder fully dissolves into a crystal-clear solution. Do not shake vigorously, as shaking causes foaming and denaturation.
Refrigerate Immediately: Store reconstituted solution between 36°F and 46°F (2°C–8°C). Protect from direct light. Once punctured, bacteriostatic water contains 0.9% benzyl alcohol which preserves sterility for up to 28 days.

Quick Reference: Common Reconstitution Recipes

Vial Strength	BAC Water Added	Concentration	0.25 mg Dose	0.5 mg Dose	1.0 mg Dose
5 mg Vial	1.0 mL	5.0 mg/mL	5 units	10 units	20 units
5 mg Vial	2.0 mL	2.5 mg/mL	10 units	20 units	40 units
10 mg Vial	2.0 mL	5.0 mg/mL	5 units	10 units	20 units
15 mg Vial	3.0 mL	5.0 mg/mL	5 units	10 units	20 units
30 mg Vial	3.0 mL	10.0 mg/mL	2.5 units	5 units	10 units

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