Peptide Reconstitution Calculator
Enter your vial size, the bacteriostatic water you added, and your target dose. Get the exact syringe units to draw.
For in vitro laboratory research calculation only. Not medical advice. Verify all figures independently before use. Syringe-unit results assume a standard U-100 insulin syringe (100 units = 1 mL).
Mess up the reconstitution math and you don’t get a slightly-off dose. You get one ten times too strong, or a vial of expensive powder you wasted because you added the wrong amount of water.
This is the single most confusing part of working with research peptides, and it’s where most people slip. So this peptide calculator and guide kill the confusion for good. Use the calculator above for the instant answer, then read below to understand exactly what it’s doing and never second-guess a draw again.
For in vitro laboratory research only. Not medical advice. Always verify your own figures.
The Three Units That Trip Everyone Up
Most peptide dosing errors come from one thing: three different unit systems showing up in the same set of instructions.
Milligrams (mg) and micrograms (mcg) measure weight. This is how much actual peptide you have. The only conversion you need: 1 mg = 1,000 mcg. Most healing peptides like BPC-157, TB-500, and GHK-Cu are dosed in micrograms, while the vial is labeled in milligrams. That mismatch is where zeros go missing.
Milliliters (mL) measure volume. This is how much liquid you’ve got after adding bacteriostatic water.
Insulin units (IU) are what’s printed on your syringe. Here’s the key fact: on a standard U-100 insulin syringe, 100 units = 1 mL. So 1 unit = 0.01 mL. Units measure volume, not weight. A “25-unit draw” is just 0.25 mL of liquid, whatever happens to be dissolved in it.
Keep those three straight and the whole thing becomes simple arithmetic.
How to Reconstitute a Peptide (Step by Step)
Peptides ship as a lyophilized (freeze-dried) powder. You have to reconstitute them, meaning add liquid, before measuring a dose.
- Gather your supplies: the peptide vial, bacteriostatic water (BAC water), alcohol swabs, and an insulin syringe.
- Swab both vial tops with alcohol to stay sterile.
- Draw your BAC water into the syringe (the calculator tells you how much to add).
- Inject the water slowly down the inside wall of the peptide vial. Never blast it directly onto the powder.
- Swirl gently to dissolve. Do not shake. Shaking can damage the peptide.
- Label the vial with the date and concentration, then refrigerate.
To read your dose, hold the syringe at eye level with the needle pointing up, and line the bottom of the curved liquid surface (the meniscus) up with your target mark.
Most reconstituted peptides stay stable refrigerated at 36 to 46°F (2 to 8°C) for roughly 4 to 6 weeks. Note that the 2026 USP 797 standard sets a more conservative 28-day beyond-use date (BUD) for compounded solutions made with bacteriostatic water, so if you want to follow the strictest published reference, treat 28 days as your outer limit.
The Reconstitution Math (Plain English)
Three steps. That’s the whole thing.
Step 1, find your concentration. Concentration = peptide amount ÷ water added. A 5 mg vial with 2 mL of BAC water = 2.5 mg/mL, which is 2,500 mcg/mL.
Step 2, find the volume to draw. Volume = target dose ÷ concentration. For a 250 mcg dose at 2,500 mcg/mL: 250 ÷ 2,500 = 0.1 mL.
Step 3, convert to syringe units. Units = volume in mL × 100. 0.1 mL × 100 = 10 units.
So a 5 mg vial reconstituted with 2 mL of water, dosed at 250 mcg, means you draw to the 10-unit mark. The calculator above runs all three steps instantly, but now you can check it by hand.
Reconstitution Reference Table
The fastest way to find a concentration without doing the math. Find your vial size, find the water you added, read the concentration.
| Vial size | + 1 mL water | + 2 mL water | + 3 mL water | + 5 mL water |
|---|---|---|---|---|
| 2 mg | 2 mg/mL | 1 mg/mL | 0.67 mg/mL | 0.4 mg/mL |
| 5 mg | 5 mg/mL | 2.5 mg/mL | 1.67 mg/mL | 1 mg/mL |
| 10 mg | 10 mg/mL | 5 mg/mL | 3.33 mg/mL | 2 mg/mL |
| 15 mg | 15 mg/mL | 7.5 mg/mL | 5 mg/mL | 3 mg/mL |
| 30 mg | 30 mg/mL | 15 mg/mL | 10 mg/mL | 6 mg/mL |
Once you have the concentration, divide your target dose by it for the mL to draw, then multiply by 100 for units on a U-100 syringe.
Common Peptide Reconstitution Examples
Quick reference for popular compounds, all using a U-100 syringe.
- BPC-157, 5 mg vial + 2 mL water = 2.5 mg/mL. A 250 mcg dose = 10 units.
- TB-500, 5 mg vial + 2 mL water = 2.5 mg/mL. A 500 mcg dose = 20 units.
- GHK-Cu, 50 mg vial + 5 mL water = 10 mg/mL. A 2 mg dose = 20 units.
- Ipamorelin, 5 mg vial + 2.5 mL water = 2 mg/mL. A 200 mcg dose = 10 units.
- CJC-1295, 2 mg vial + 2 mL water = 1 mg/mL. A 100 mcg dose = 10 units.
- Tesamorelin, 5 mg vial + 2 mL water = 2.5 mg/mL. A 1 mg dose = 40 units.
- PT-141, 10 mg vial + 2 mL water = 5 mg/mL. A 1 mg dose = 20 units.
- Semaglutide, 5 mg vial + 1 mL water = 5 mg/mL. A 250 mcg dose = 5 units.
- Tirzepatide, 10 mg vial + 2 mL water = 5 mg/mL. A 2.5 mg dose = 50 units.
- Retatrutide, 10 mg vial + 2 mL water = 5 mg/mL. A 2 mg dose = 40 units.
Plug any of these into the calculator to confirm.
Using a Refillable Pen Instead of a Syringe
A lot of GLP-1 researchers (semaglutide, tirzepatide, retatrutide) load their solution into a refillable injector pen instead of drawing with a syringe. The reconstitution math is identical. The only difference is the final step.
You still reconstitute the same way and find your draw volume in mL. Then, instead of converting to syringe units, you dial the pen to that mL volume. Most refillable pens click in 0.01 mL or 0.02 mL increments, so set the dial to the mL figure the calculator gives you. Reconstitute the vial, transfer the solution into the pen cartridge with a syringe, then dose by the dial. Same concentration math, different delivery device.
How Much Bacteriostatic Water Should You Add?
There’s no single “right” amount of BAC water. More water doesn’t change how much peptide you have, it just changes the concentration, and therefore how many units you draw.
Add less water and you get a concentrated solution, so each dose is a small number of units. Add more water and the solution is dilute, so the same dose takes more units. The trick experienced researchers use: pick a water amount that makes your target dose land on a clean, easy-to-read number like 10, 20, or 50 units. That minimizes misreads.
If you accidentally add too much water, nothing is ruined. The peptide is fine. You’ve just made a weaker concentration, so you draw a larger volume per dose. Re-run the calculator with the actual water amount and you’re set.
The Mistakes That Cause Real Damage
These are the errors that show up over and over.
Reading mg as mcg (or vice versa). A 12.5 mg dose is 12,500 mcg. Confuse the two and you’re off by a factor of 1,000. Always check the unit on both the product sheet and the dose instruction before doing any math.
Wrong water volume. Adding 1 mL when the plan was 2 mL doubles your concentration and halves the units you should draw. If a result looks strange, recheck the water entry first.
Syringe mismatch. Getting the dose right but drawing on the wrong syringe size still leads to errors. Know whether you’re on a 30, 50, or 100-unit syringe.
Converting mid-calculation. This is where zeros vanish. Stick to one unit system the whole way through. If your peptide is dosed in mcg, keep everything in mcg until the final answer.
IU confusion on HCG and HGH. A handful of compounds (HCG, HGH-class) are dosed in true International Units of potency, which is different from the volume units on your syringe. For everything else, mcg or mg is what you want. Don’t mix the two ideas.
Where to Get Quality Research Peptides
Accurate dosing math only matters if the peptide in the vial is actually what the label says. A perfect calculation on an underdosed or mislabeled vial still gives you the wrong result. Independent testing has found a large share of online peptides come in underdosed or contaminated, so the source matters as much as the math.
Before you reconstitute anything, make sure it came from a vendor with batch-specific, third-party Certificates of Analysis you can verify. Start with our verified peptide vendors list and check our fake vendor red flags first.
Conclusion
Peptide dosing math feels intimidating, but it’s three steps of arithmetic once you separate weight (mg/mcg), volume (mL), and syringe units. Concentration first, volume second, units third. Use the calculator at the top for the instant answer, double-check it by hand the first few times, and you’ll never misdose from confusion again.
And remember: the cleanest math in the world can’t fix a bad vial. Start with a third-party-tested source, then calculate with confidence.
How do I calculate peptide dosage?
Find your concentration (vial amount ÷ water added), divide your target dose by that concentration to get the volume in mL, then multiply by 100 for the units on a U-100 insulin syringe. The calculator above does all three steps automatically.
How many units is a 250 mcg dose of BPC-157?
With a 5 mg vial reconstituted in 2 mL of bacteriostatic water (2.5 mg/mL), a 250 mcg dose equals 10 units on a U-100 insulin syringe.
How much bacteriostatic water do I add to a peptide vial?
There’s no fixed amount. Most researchers use 1 to 3 mL and choose the volume that makes their target dose land on a round syringe number. More water means a more dilute solution and a larger draw per dose.
What does 100 units mean on an insulin syringe?
On a standard U-100 syringe, 100 units equals 1 mL of total volume. So 10 units is 0.1 mL and 50 units is 0.5 mL. Units measure liquid volume, not the weight of peptide.
What’s the difference between mg, mcg, and IU?
Mg and mcg are weight (1 mg = 1,000 mcg). IU is either a potency unit (for HCG and HGH-class compounds) or, on a syringe, a volume marking. Most research peptides are dosed in mcg or mg.
Can I add too much water when reconstituting?
Yes, but it doesn’t ruin the peptide. Extra water just makes a weaker solution, so each dose takes more units. Recalculate with the actual water volume you used.
How long does reconstituted peptide last?
Stored refrigerated at 36 to 46°F (2 to 8°C), most reconstituted peptides stay stable for about 4 to 6 weeks. Keep the vial upright and protected from light.
The Bottom Line
Peptide dosing math feels intimidating, but it’s three steps of arithmetic once you separate weight (mg/mcg), volume (mL), and syringe units. Concentration first, volume second, units third. Use the calculator at the top for the instant answer, double-check it by hand the first few times, and you’ll never misdose from confusion again.
And remember: the cleanest math in the world can’t fix a bad vial. Start with a third-party-tested source, then calculate with confidence.