This peptide reconstitution calculator tells you exactly how many units to draw after mixing your vial.

Enter the vial size, how much bacteriostatic water you added, and the dose you want —

you get the units, the volume in mL, the concentration, and how many doses your vial holds.

Peptide reconstitution chart

The chart below shows the concentration you get for the two most common vial sizes. Concentration is simply the vial amount divided by the water added.

Vial size	1 mL water	2 mL water	3 mL water
5 mg	5 mg/mL	2.5 mg/mL	1.67 mg/mL
10 mg	10 mg/mL	5 mg/mL	3.33 mg/mL

Example: a 250 mcg dose from a 5 mg vial mixed with 2 mL of water (2.5 mg/mL) is 0.1 mL — exactly 10 units on a U-100 syringe.

How to reconstitute peptides (step by step)

Step 1: Clean everything first

Good technique starts with a clean setup. Wash your hands with soap and water, then dry them completely. Wipe the rubber stopper on top of the peptide vial and the stopper on the bacteriostatic water vial, using a fresh alcohol swab for each one. Let the alcohol evaporate fully before inserting a needle. Work on a clean, flat, stable surface, and keep the vials, syringe and swabs within easy reach so nothing has to be set down on an unclean area partway through.

Step 2: Draw the bacteriostatic water

Decide on the water volume before you begin, because the final concentration depends entirely on this number. A common example is 2 mL of bacteriostatic water for a 5 mg vial, which gives a concentration of 2.5 mg/mL. Before drawing, push a small amount of air into the water vial to equalize the pressure, which makes the liquid easier to pull out. Draw the exact planned amount, then check the syringe barrel at eye level to confirm the reading.

Step 3: Add the water slowly, down the wall

Insert the needle into the peptide vial at an angle so the tip points toward the inside glass wall. Press the plunger slowly and let the water run gently down the wall until it reaches the powder. Never spray water directly onto the freeze-dried powder cake, and never shake the vial. A hard stream or vigorous shaking can damage the delicate peptide chains and create foam, and foam also makes accurate measuring harder.

Step 4: Swirl gently until clear

Once the water is in, gently roll the vial between your fingers and swirl it in slow circles. Most lyophilized peptides dissolve within a few minutes into a clear solution. If some powder is slow to dissolve, the vial can rest in the fridge for a short time and then be swirled again. If the solution stays cloudy or shows visible particles after mixing, do not use it.

Step 5: Store it correctly

Store the reconstituted peptide in the fridge at 2–8 °C, away from the freezer section and out of direct light. Never freeze a peptide once it has been mixed with water. Write the mixing date and the concentration on the vial label so the correct numbers are always on hand when you use the peptide calculator. Most reconstituted peptides are generally used within about four weeks of mixing.

Frequently asked questions

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

2 mL is the most common choice: it gives a 2.5 mg/mL concentration, so a 250 mcg dose is exactly 10 units. Adding 1 mL makes it stronger (5 mg/mL, 5

units per 250 mcg); adding 3 mL makes each dose easier to measure but larger in volume.

How long does a reconstituted peptide last?

Kept refrigerated at 2–8 °C, most reconstituted peptides are used within about 4 weeks.

Always follow your supplier's guidance, and do not use the solution if it turns cloudy or shows particles.

Can I use sterile water instead of bacteriostatic water?

Sterile water has no preservative, so it is only suited to a single immediate use.

For a vial you will draw from over several weeks, bacteriostatic water is the standard choice.

Why is my peptide not dissolving?

Give it time — let the water run down the vial wall and swirl gently.

Most lyophilized peptides clear within a few minutes. Never shake the vial, as foaming can damage the peptide.

For research and educational purposes only. This calculator is a math tool, not medical advice.