Peptide Dosage Calculator

How to Calculate Peptide Dosage from Syringe Units

This peptide dosage calculator converts your dose in mg or mcg to exact insulin syringe units — no manual math required. When you reconstitute a lyophilized peptide vial with bacteriostatic (BAC) water, you create a solution with a specific concentration in micrograms per milliliter (mcg/mL). To dose using an insulin syringe, you need to know how many syringe "units" correspond to your target dose in mcg.

The formula has two steps:

1. Concentration (mcg/mL) = Vial size (mg) × 1,000 ÷ BAC water volume (mL)
2. Dose (mcg) = Units drawn ÷ Syringe factor × Concentration

The syringe factor is 100 for U-100 syringes (100 units per mL) and 40 for U-40 syringes (40 units per mL). For example, a 5 mg vial with 2 mL of BAC water gives a concentration of 2,500 mcg/mL. Drawing 10 units on a U-100 syringe = 10/100 = 0.1 mL × 2,500 = 250 mcg.

Reconstitution Guide: Choosing Your BAC Water Volume

The amount of BAC water you add determines your concentration and affects dosing precision. Here are common configurations for a 5 mg peptide vial:

• 1 mL BAC water: 5,000 mcg/mL — each unit on U-100 = 50 mcg. Very concentrated; small volume differences matter more.
• 2 mL BAC water: 2,500 mcg/mL — each unit on U-100 = 25 mcg. The most common choice.
• 5 mL BAC water: 1,000 mcg/mL — each unit on U-100 = 10 mcg. Easier to measure small doses precisely.

Choose a volume that puts your typical dose in the 10–50 unit range on the syringe for the most accurate measurement. Very small unit draws (1–2 units) introduce proportionally higher measurement error.

U-100 vs. U-40 Syringes: An Important Distinction

U-100 and U-40 refer to the calibration of the syringe, not any property of the peptide itself. A U-100 syringe assumes 100 units of insulin per mL — meaning 1 unit mark = 0.01 mL. A U-40 syringe (older, now rare in the US, still used in some countries) assumes 40 units per mL — meaning 1 unit mark = 0.025 mL. This 2.5× difference means that drawing 10 units on a U-40 syringe delivers 2.5× the volume of 10 units on a U-100 syringe, resulting in a 2.5× different dose from the same vial.

Always verify your syringe type before drawing. Using a U-40 syringe when a protocol calls for U-100 dosing (or vice versa) is a common source of dosing errors.

Retatrutide Dosage Examples

Retatrutide is a GLP-1/GIP/glucagon triple agonist research peptide with doses measured in milligrams per week. Converting those to syringe units requires knowing your vial concentration. For protocol-specific dose guidance, see the retatrutide dosage calculator. Here are worked examples using a 5 mg vial reconstituted with 2 mL BAC water (concentration = 2,500 mcg/mL, 25 mcg per U-100 unit):

• 2 mg/week (2,000 mcg): 2,000 ÷ 2,500 × 100 = 80 units on U-100
• 4 mg/week (4,000 mcg): 4,000 ÷ 2,500 × 100 = 160 units on U-100
• 8 mg/week (8,000 mcg): 8,000 ÷ 2,500 × 100 = 320 units on U-100 (split into multiple syringes or use a higher concentration)
• 12 mg/week (12,000 mcg): best reconstituted as 5,000 mcg/mL (5 mg + 1 mL) to keep draw volume manageable — 12,000 ÷ 5,000 × 100 = 240 units

For higher weekly doses, reconstituting at higher concentration (1 mL BAC water per 5 mg) reduces injection volume. Use the peptide reconstitution calculator to find the right BAC water volume for your dose.

Reverse Calculation: Units to Draw for a Target Dose

Use the "mcg → Units" tab to work backwards: enter your desired dose in mcg, and the calculator tells you how many units to draw. This is useful when you know the target dose from a protocol but need to translate it to syringe marks.

Safe Handling and Storage

Reconstituted peptides should be refrigerated at 2–8°C and used within 28–56 days. Always use aseptic technique — wipe the rubber stopper with an alcohol swab before each injection. Use a fresh needle for each injection. Never inject cloudy or particulate solutions. Dispose of needles and syringes in a sharps container.

Common Peptide Dosing Mistakes to Avoid

Even with the math correct, handling errors can lead to dosing mistakes or compromised product quality. The most common mistakes:

• Shaking the vial instead of swirling: Vigorous shaking creates bubbles and mechanical stress that can denature peptide bonds. Always gently swirl or roll the vial to dissolve the powder.
• Using the wrong syringe type: Mixing up U-100 and U-40 syringes results in a 2.5× dosing error. Always verify syringe type before drawing.
• Drawing up air bubbles: Inject air into the vial first to equalize pressure, then draw the solution. If bubbles appear, tap the syringe and push them out before injecting.
• Not wiping the stopper: Use a 70% isopropyl alcohol swab on the rubber septum before every draw and every injection to maintain sterility.
• Storing reconstituted peptide in the freezer: Freeze-thaw cycles degrade peptide structure. Once reconstituted, refrigerate only.

What Is Bacteriostatic Water and Why Use It?

Bacteriostatic water (BAC water) is sterile water for injection containing 0.9% benzyl alcohol. The benzyl alcohol is a preservative that inhibits bacterial growth, allowing the reconstituted solution to be stored in the refrigerator and re-used from the same vial multiple times over 28+ days. This makes it the standard diluent for multi-dose peptide vials.

Regular sterile water for injection (without benzyl alcohol) is appropriate only for single-use preparation — the solution must be used within 24 hours and discarded. BAC water is widely available from compounding pharmacies, medical supply companies, and online retailers. It is sold in 30 mL bacteriostatic vials designed for multi-use reconstitution. For more detail on how different BAC water volumes affect concentration and dosing, see the companion peptide reconstitution calculator.