Peptide Reconstitution Calculator

How Peptide Reconstitution Works

This peptide reconstitution calculator shows exactly how much BAC water to add and what syringe units to draw. Lyophilized (freeze-dried) peptides are supplied as powder in sealed vials. Before injection, the powder must be dissolved in a liquid — typically bacteriostatic water (BAC water) for multi-use vials. The resulting solution has a specific concentration measured in micrograms per milliliter (mcg/mL), which determines how much to draw per dose.

The reconstitution process is straightforward: inject BAC water slowly down the side of the vial (not directly onto the powder), then gently swirl — never shake — until fully dissolved. The solution should be clear; discard if cloudy or particulate matter is present.

Understanding the Concentration Formula

Concentration (mcg/mL) = Peptide (mg) × 1000 ÷ BAC Water (mL)

The ×1000 converts milligrams to micrograms. For a 5 mg vial with 2 mL BAC water: 5 × 1000 ÷ 2 = 2500 mcg/mL. For the same vial with 1 mL BAC water: 5000 mcg/mL — twice the concentration, so half the injection volume per dose.

Reading an Insulin Syringe for Peptide Dosing

Peptides are injected subcutaneously using insulin syringes due to the small volumes involved. The two most common types are:

• U-100: 100 units per mL (1 unit = 0.01 mL) — the standard in the US
• U-40: 40 units per mL (1 unit = 0.025 mL) — common in some countries

The calculator converts your desired dose in mcg to the exact number of syringe units for each type: U-100 units = (Dose mcg ÷ Concentration mcg/mL) × 100. For example, a 250 mcg dose from 2500 mcg/mL solution: volume = 0.1 mL = 10 units on a U-100 syringe.

Choosing BAC Water Volume

The volume of BAC water you add affects injection volume per dose. A lower concentration (more BAC water) produces larger injection volumes — easier to measure precisely but more liquid per injection. A higher concentration (less BAC water) produces smaller volumes — less discomfort per injection but harder to measure small doses accurately.

Common guidelines for practical use: for doses of 250–500 mcg, adding 1–2 mL BAC water to a 5 mg vial gives 10–20 units on a U-100 syringe per dose, which is easy to draw up accurately. Use our dosage calculator for additional drug calculation modes.

Retatrutide Reconstitution Guide

Retatrutide (LY3437943) is a triple agonist research peptide — it targets GLP-1, GIP, and glucagon receptors simultaneously. It is supplied as a lyophilized powder and reconstituted with BAC water using the same technique as any other peptide. Vial sizes typically range from 2 mg to 10 mg. Below are the most common reconstitution configurations:

• 2 mg vial + 1 mL BAC water: 2,000 mcg/mL — 20 mcg per unit on U-100
• 5 mg vial + 1 mL BAC water: 5,000 mcg/mL — 50 mcg per unit on U-100
• 5 mg vial + 2 mL BAC water: 2,500 mcg/mL — 25 mcg per unit on U-100
• 10 mg vial + 2 mL BAC water: 5,000 mcg/mL — 50 mcg per unit on U-100

Weekly doses in research settings range from 2 mg (2,000 mcg) up to 12 mg (12,000 mcg). Use the calculator above to convert any dose-to-units combination instantly, or use the peptide dosage calculator to work from a target dose in mcg directly to syringe units. Store reconstituted retatrutide refrigerated at 2–8°C and use within 28 days.

Storage and Stability

After reconstitution with BAC water, peptides should be refrigerated at 2–8°C and used within 28 days. Keep the vial upright and minimize light exposure. The benzyl alcohol in BAC water prevents bacterial growth over this period. Sterile water (without preservative) limits shelf life to 24 hours and is not recommended for multi-dose use.

Unreconstituted lyophilized peptide powder should be stored frozen at −20°C or lower for long-term storage, or refrigerated if use within 1–3 months is planned. Temperature-sensitive peptides should always be shipped with cold packs and may have specific storage requirements from the manufacturer. Consult a licensed healthcare provider before use.

Step-by-Step Reconstitution Protocol

Proper aseptic technique minimizes contamination risk and ensures the solution remains sterile for its full shelf life:

1. Wash hands thoroughly with soap and water.
2. Gather materials: peptide vial, BAC water vial, insulin syringe, alcohol swabs, and a clean surface.
3. Wipe both vial stoppers with separate alcohol swabs and allow to air dry for 30 seconds.
4. Draw the desired BAC water volume into the syringe (e.g., 2 mL for a 5 mg vial).
5. Insert the needle into the peptide vial and slowly inject the BAC water down the inside wall — not directly onto the powder cake.
6. Gently swirl (do not shake) until the powder fully dissolves. The solution should be clear.
7. Label the vial with the reconstitution date and concentration (e.g., "2,500 mcg/mL, June 2, 2026").
8. Refrigerate immediately at 2–8°C. Use within 28 days.

Lyophilization: Why Peptides Come as Powder

Lyophilization (freeze-drying) is the standard manufacturing process for injectable peptides because peptide bonds are chemically unstable in aqueous solution over time — particularly at room temperature. The process involves freezing the solution, then reducing pressure to allow the ice to sublimate (convert directly to water vapor) without melting, leaving behind a stable dry powder. This powder can be stored for months to years frozen without significant degradation, making distribution and storage practical. Once water is reintroduced during reconstitution, the stability clock restarts — hence the 28-day refrigerated shelf life. For dosing math after reconstitution, the peptide dosage calculator handles the unit-to-mcg conversion instantly.