What reconstitution is, and why you do it
Most research peptides ship as a lyophilized (freeze-dried) powder sealed in a small glass vial. Powder is stable and easy to ship, but you cannot measure a powder dose accurately by eye. Reconstitution is the step that turns that powder into a liquid you can actually draw into a syringe.
To do it, you mix the powder with bacteriostatic water (often called BAC water). That is sterile water with benzyl alcohol added as a preservative, which is what lets you use the same vial for multiple doses over time. Once you know how much water you added, the rest is simple division.
This guide is research-use-only and educational. Dosing here describes what the research and community commonly use, not a prescription or medical advice. Nothing on Clearly Peptides is sold by us. We compare third-party vendor prices and publish real per-batch lab data so you can see what you are buying.
The only formula you need
Everything comes down to concentration, which is how much peptide sits in each milliliter of liquid after you mix.
Step 1: concentration
If you put 2 mL of BAC water into a 10 mg vial, that is 10 / 2 = 5 mg/mL. The peptide is now evenly spread through the liquid.
Step 2: volume to draw
One thing trips almost everyone up: units. Doses are usually written in micrograms (mcg) but concentration is in milligrams (mg). Convert first.
A fully worked example
Say you have a 10 mg vial and you add 2 mL of BAC water, and your target dose is 250 mcg.
- Concentration: 10 mg / 2 mL = 5 mg/mL.
- Convert the dose: 250 mcg = 0.25 mg.
- Volume to draw: 0.25 mg / 5 mg/mL = 0.05 mL.
- On a U-100 insulin syringe, 0.05 mL = 5 units (more on that below).
You can also work out how long a vial lasts. Doses per vial = vial mg / dose mg. Here that is 10 / 0.25 = 40 doses from one vial.
Here are a couple of common setups side by side so you can see the pattern:
| Vial | Water | Concentration | Dose | Volume | On syringe |
|---|---|---|---|---|---|
| 10 mg | 2 mL | 5 mg/mL | 250 mcg | 0.05 mL | 5 units |
| 5 mg | 2 mL | 2.5 mg/mL | 200 mcg | 0.08 mL | 8 units |
The second row is the same arithmetic: 5 / 2 = 2.5 mg/mL, and 0.2 mg / 2.5 mg/mL = 0.08 mL, which is 8 units.
Reading an insulin syringe: units vs mL
Insulin syringes are marked in units, not milliliters, and most are U-100. That is the only conversion you need:
This is why so many people second-guess themselves: the calculator gives you a volume in mL, but the lines on the barrel say units. Multiply the mL by 100 and read that many units.
Why the water amount changes the units but not the dose
This is the part worth slowing down on. Imagine the same 10 mg vial, but you add 4 mL of water instead of 2 mL. Now the concentration is 10 / 4 = 2.5 mg/mL, which is more dilute. To get the same 250 mcg dose you draw 0.25 / 2.5 = 0.1 mL, which is 10 units instead of 5.
Notice what did and did not change. You are still delivering exactly 250 mcg of peptide. More water did not make the dose weaker or stronger. It just spread the same peptide across more liquid, so you draw a larger volume to capture the same amount.
- More water = lower concentration = more units to draw, but the same dose.
- Less water = higher concentration = fewer units to draw, but the same dose.
- The dose is set by the powder in the vial, not by how much water you add.
Some people prefer a little more water so the units are easier to read on the syringe. That is a personal preference, not a change to your dose.
Common mistakes to avoid
- Mixing up mcg and mg. This is the big one. A 10x error here means a 10x error in your dose. Always convert to the same unit before dividing: 1000 mcg = 1 mg.
- Adding the wrong amount of water. It will not ruin the peptide, but it changes the concentration, so it changes how many units you draw. Write down exactly how much water you added so your math matches reality.
- Reading the syringe in mL when it is marked in units. Remember units = mL × 100.
- Injecting too fast. A slow, steady push is more comfortable and reduces irritation at the site.
- Storing it wrong. Powder can sit at room temperature before you mix it, but once reconstituted it goes in the fridge.
Frequently asked.
How much bacteriostatic water do I add to a peptide vial?
There is no single correct amount. The water sets the concentration, not the dose. A common choice is 2 mL: in a 10 mg vial that gives 5 mg/mL, and in a 5 mg vial it gives 2.5 mg/mL. More water means you draw more units for the same dose; less water means fewer units. Pick an amount that makes the syringe easy to read, then run it through the calculator.
How many units is 250 mcg?
It depends on your concentration. With a 10 mg vial reconstituted in 2 mL (5 mg/mL), 250 mcg works out to 0.05 mL, which is 5 units on a U-100 insulin syringe. Change the water amount and the units change, even though the dose stays at 250 mcg. The calculator gives you the exact units for your setup.
Does more water mean a stronger dose?
No. The dose is set by the peptide powder in the vial, not by how much water you add. More water makes the liquid more dilute, so you draw a larger volume (more units) to get the same amount of peptide. The milligrams or micrograms delivered do not change.
How long does reconstituted peptide last?
Once mixed, reconstituted peptides should be kept in the fridge. The dry powder is more stable and can sit at room temperature before you mix it. Using bacteriostatic water rather than plain sterile water matters here, because its preservative is what makes a multi-dose vial workable over time. Always follow the storage guidance from your specific vendor.
What is the difference between mcg and mg in dosing?
They are the same kind of unit at different scales: 1000 mcg = 1 mg. Doses are often written in mcg while vial sizes and concentration are in mg, so you have to convert before dividing. Mixing them up is the most common and most serious reconstitution error, because it can throw your dose off by a factor of ten.