Peptide dosage calculation comes down to three numbers: how much peptide is in your vial, how much water you added, and how many micrograms you need per dose. Once you understand the relationship between these three values, every peptide calculation becomes straightforward.
The Core Formula
Every peptide dosage calculation uses this formula:
But before you can use that, you need to know your concentration — and that depends on reconstitution.
Step 1: Know Your Vial
Every peptide vial has a total amount printed on the label, usually in milligrams. Common examples:
- BPC-157: typically 5mg per vial
- TB-500: typically 5mg or 10mg per vial
- Ipamorelin: typically 5mg per vial
- Semaglutide: typically 5mg per vial
This number is fixed. It tells you the total amount of peptide in the entire vial before you add any water.
Step 2: Reconstitute and Calculate Concentration
When you add bacteriostatic water to the vial, you create a solution with a specific concentration. The amount of water you add determines how concentrated the solution is.
For example, with a 5mg vial:
- Add 1mL of water: 5mg/mL (5,000 mcg/mL)
- Add 2mL of water: 2.5mg/mL (2,500 mcg/mL)
- Add 2.5mL of water: 2mg/mL (2,000 mcg/mL)
Less water = more concentrated solution. More water = more dilute, but easier to measure small doses accurately.
Step 3: Convert to Syringe Units
Standard insulin syringes hold 1mL total and are marked in 100 units. So:
- 100 units = 1mL
- 50 units = 0.5mL
- 10 units = 0.1mL
- 1 unit = 0.01mL
Once you know your concentration per mL, divide by 100 to get mcg per unit on the syringe.
Step 4: Calculate Your Dose
Here is a real example. You have a 5mg BPC-157 vial and you want a 250mcg dose.
- Add 2mL bacteriostatic water to the 5mg vial
- Concentration = 5,000mcg / 2mL = 2,500mcg per mL
- Per syringe unit = 2,500 / 100 = 25mcg per unit
- For 250mcg: 250 / 25 = 10 units on the syringe
Common Mistakes to Avoid
Confusing mg and mcg. 1mg = 1,000mcg. A 250mcg dose is 0.25mg. Mixing these up leads to 1,000x dosing errors — always double-check your units.
Using the wrong syringe. Standard U-100 insulin syringes have 100 units per mL. U-40 syringes exist for veterinary use and have different markings. Make sure you are using U-100.
Not accounting for water already in the vial. The lyophilized powder takes up negligible volume. Your concentration is based on the water you add, not total vial volume.
Quick Reference Table
For a 5mg vial with different water volumes:
| Water Added | Concentration | MCG per Unit | Units for 250mcg |
|---|---|---|---|
| 1mL | 5,000 mcg/mL | 50 mcg | 5 units |
| 2mL | 2,500 mcg/mL | 25 mcg | 10 units |
| 2.5mL | 2,000 mcg/mL | 20 mcg | 12.5 units |
| 5mL | 1,000 mcg/mL | 10 mcg | 25 units |
Adding more water makes it easier to measure small doses precisely, but you will need to inject more volume per dose.
Use the Calculator
If you prefer to skip the math, our reconstitution calculator handles the concentration calculation, and the dosage calculator tells you exactly how many units to draw. Enter your vial size, water volume, and desired dose — the tools do the rest.