How to Calculate Peptide Concentration After Reconstitution

Peptides come as a dry powder in a vial. Before you can use them in research, you add liquid — usually bacteriostatic water — to dissolve the powder. This is called reconstitution. Once you reconstitute, you have a liquid solution with a specific concentration. Getting that concentration right is essential for reproducible research.

What You Need to Know Before You Calculate

There are three pieces of information you always need:

1. How much peptide is in the vial — stated on the label (e.g., 5mg = 5000mcg)
2. How much bacteriostatic water you added — this is your choice during reconstitution
3. What volume you want to draw per dose — typically measured in units on an insulin syringe

View Bacteriostatic Water →

The Core Formula

Here is the calculation you will use every time:

Step 1: Convert vial amount to mcg
5mg = 5000mcg
10mg = 10,000mcg

Step 2: Calculate concentration in mcg/mL
Concentration = Total mcg ÷ mL of water added

Step 3: Calculate mcg per unit (for insulin syringe)
Mcg per unit = Concentration ÷ 100

An insulin syringe holds 1mL and is marked in 100 units. So 1 unit = 0.01mL. This is why you divide by 100.

Worked Examples

Example 1: 5mg vial + 2mL bacteriostatic water

Total peptide: 5mg = 5000mcg
Water added: 2mL
Concentration: 5000 ÷ 2 = 2500mcg/mL
Mcg per unit: 2500 ÷ 100 = 25mcg per unit

So if a research protocol calls for 250mcg, you would draw 10 units on the syringe.

Example 2: 10mg vial + 2mL bacteriostatic water

Total peptide: 10mg = 10,000mcg
Water added: 2mL
Concentration: 10,000 ÷ 2 = 5000mcg/mL
Mcg per unit: 5000 ÷ 100 = 50mcg per unit

A 500mcg dose would require 10 units on the syringe.

Example 3: 5mg vial + 1mL bacteriostatic water

Total peptide: 5000mcg
Water added: 1mL
Concentration: 5000 ÷ 1 = 5000mcg/mL
Mcg per unit: 5000 ÷ 100 = 50mcg per unit

Adding less water makes the solution more concentrated — smaller volumes per dose.

The Quick Reference Table

How Much Water Should You Add?

There is no single right answer. More water means a less concentrated solution, which means larger volumes per dose. Less water means smaller volumes per dose. Both work — it comes down to your protocol’s preferred dose volumes.

Most researchers use 1mL to 2mL for a 5mg vial. This gives manageable concentrations and doesn’t require drawing very small volumes (which reduces pipetting error).

Storing Reconstituted Peptides

Once reconstituted with bacteriostatic water, most peptides are stable in a refrigerator for 4-6 weeks. Bacteriostatic water contains benzyl alcohol which inhibits bacterial growth. Never use plain sterile water — it has no preservative and reconstituted peptides will degrade quickly.

Summary of Key Research References

Written by the NorthPeptide Research Team