Peptide Reconstitution Calculator

Research-grade reconstitution math for any peptide vial. Enter your vial size, bacteriostatic water volume, and target research dose — get the exact draw in IU and ml.

TL;DR: Concentration (mcg/ml) = vial mg × 1000 ÷ bacteriostatic water ml. Draw (ml) = dose mcg ÷ concentration. On a U-100 insulin syringe, units = draw ml × 100. Example: 5 mg BPC-157 + 2 ml BAC water = 2,500 mcg/ml; a 250 mcg research dose draws 0.10 ml = 10 IU.

What reconstitution is and when you need it

Research peptides ship as a lyophilized (freeze-dried) powder inside a sealed vial. The powder is stable at room temperature for short windows and under refrigeration for much longer, but it is not measurable or injectable in solid form. Reconstitution is the lab procedure of dissolving that powder into a measured volume of sterile solvent — almost always bacteriostatic water (sterile water with 0.9% benzyl alcohol as a preservative) — so that the peptide can be drawn accurately with a syringe.

Because the vial label only tells you the total mass of peptide (for example, "5 mg" or "10 mg"), the researcher has to decide how much water to add. That decision sets the concentration of the resulting solution, and concentration is what turns a target dose in micrograms into a specific mark on a syringe. Reconstitution math is the bridge between the label and the barrel.

You need a calculator the moment you vary any of three things: the vial size (5 mg vs. 10 mg vs. 20 mg), the volume of bacteriostatic water you add (1 ml, 2 ml, 3 ml), or the target research dose (250 mcg of BPC-157 looks nothing like 2,500 mcg of Tirzepatide on the same syringe). Doing this by hand is error-prone — the calculator above does it deterministically.

How the math works

Every reconstitution calculation rests on three lines of arithmetic:

Concentration (mcg/ml) = (vial mg × 1000) ÷ bacteriostatic water ml
Volume to draw (ml) = target dose mcg ÷ concentration mcg/ml
Insulin-syringe units (IU on a U-100) = volume to draw (ml) × 100

The first line converts the vial mass to micrograms (×1000) and divides by water volume. The second line is the whole point: once you know how many micrograms sit in each milliliter of solution, a target dose divides cleanly into a volume. The third line only matters because almost all peptide work uses U-100 insulin syringes, which are marked in "units" rather than milliliters — 100 units on a U-100 syringe is exactly 1 ml, so the conversion is a flat multiply by 100.

A useful sanity check: if the resulting IU number is larger than your syringe's capacity, you either need a larger syringe, a higher concentration (less water next time), or to split the dose. The calculator flags this for you in red.

Vial strength, BAC water, and syringe type — what each input means

Vial strength is the total mass of peptide the manufacturer lyophilized into the vial, printed on the label as milligrams (mg). It does not change with reconstitution — adding water only changes concentration, never total mass. If your certificate of analysis lists a slightly different mass than the label (common with overfill), trust the COA.

Bacteriostatic water (BAC water) is sterile water containing 0.9% benzyl alcohol. The preservative suppresses microbial growth in multi-use vials — the same reason it is specified for reconstituting many injectable pharmaceuticals. Plain sterile water or 0.9% saline can also dissolve peptides but do not offer the same shelf life once pierced. Volume choices of 1 ml, 2 ml, or 3 ml are common; the calculator accepts any positive number.

Syringe type on this calculator refers to U-100 insulin syringes in three common barrel sizes: 1 ml (100 IU), 0.5 ml (50 IU), and 0.3 ml (30 IU). "U-100" describes the scale, not the barrel — all three measure the same concentration, but smaller barrels put more tick marks per unit, which matters when your draw is a handful of IU. Pick the smallest barrel whose capacity exceeds your draw.

Worked examples

Example 1 — 5 mg BPC-157 with 2 ml BAC water

A standard 5 mg vial of BPC-157 reconstituted with 2 ml of bacteriostatic water yields 2,500 mcg/ml (5 × 1000 ÷ 2). A 250 mcg research dose draws 0.10 ml, which reads as 10 IU on any U-100 insulin syringe. A single 5 mg vial at that concentration contains 20 doses of 250 mcg.

Example 2 — 10 mg BPC-157 with 2 ml BAC water

Double the vial mass without doubling the water, and concentration doubles: 10 mg ÷ 2 ml = 5,000 mcg/ml. The same 250 mcg target now draws 0.05 ml — only 5 IU. At 5 IU you may prefer a 0.3 ml (30 IU) barrel so the mark is easier to read.

Example 3 — 5 mg Semaglutide with 2 ml BAC water

A 5 mg Semaglutide vial with 2 ml of BAC water gives 2,500 mcg/ml. A 250 mcg research dose draws 0.10 ml = 10 IU. If the research protocol calls for 500 mcg, the draw becomes 0.20 ml = 20 IU; for 1,000 mcg, 0.40 ml = 40 IU.

Example 4 — 10 mg Retatrutide with 2 ml BAC water

A 10 mg Retatrutide vial reconstituted with 2 ml gives 5,000 mcg/ml. A 2,000 mcg (2 mg) research reference dose draws 0.40 ml = 40 IU. At this concentration, a single 10 mg vial contains five 2,000 mcg doses or ten 1,000 mcg doses.

Example 5 — 10 mg Tirzepatide with 3 ml BAC water

Some researchers prefer adding 3 ml of BAC water to a 10 mg vial to extend the measurable range of smaller doses. 10 × 1000 ÷ 3 ≈ 3,333 mcg/ml. A 2,500 mcg dose of Tirzepatide draws 0.75 ml = 75 IU — near the top of a 1 ml insulin syringe. Cutting water back to 2 ml would push the same dose to 50 IU on a 0.5 ml barrel.

Choosing your water volume

Water volume is a dial, not a decree. Adding more bacteriostatic water lowers concentration, which spreads each dose across more IU and makes small draws easier to read — useful for low-dose compounds like Ipamorelin or GHK-Cu. Adding less water raises concentration and shrinks injection volume, which matters for high-milligram protocols like some GLP-1 references where a dilute solution would exceed syringe capacity.

A defensible default for most 5-10 mg vials is 2 ml of BAC water. If your target draw regularly lands under 5 IU, reduce water on the next vial; if it regularly lands above 50 IU, add more.

Common mistakes

Confusing mg and mcg. 1 mg = 1,000 mcg. Vial labels are in mg, research doses are often in mcg. The calculator's concentration output is in mcg/ml to match.
Assuming "units" means international units. On a U-100 insulin syringe "IU" is a volume mark, not a biological activity unit. 10 IU is simply 0.10 ml.
Shaking the vial. Peptides are sensitive proteins — inject the BAC water slowly against the side of the vial and swirl gently. Vigorous shaking can denature the compound.
Drawing from a cold vial immediately. Letting a refrigerated vial warm for a minute in the hand makes the solution easier to draw and measure.
Forgetting which water volume was used. Label the vial. The calculator is only correct if the inputs are correct.

Storage and handling reference

Lyophilized peptides are typically stored at -20 degrees Celsius for long-term lab storage or 2-8 degrees Celsius short-term. Once reconstituted with bacteriostatic water, most peptides are refrigerated and drawn over a period of weeks; exact shelf life varies by compound and is listed on the certificate of analysis. Keep vials out of direct light. Our how-to-reconstitute guide and storage guide cover handling in more depth.

Related research references

BPC-157 — standard 5 mg vials, low-microgram research doses.
Semaglutide — 5 mg GLP-1 reference compound.
Tirzepatide — 10 mg dual GLP-1/GIP reference.
Retatrutide — 10 mg triple-agonist reference.
CJC-1295 / Ipamorelin — GH secretagogue blend.
GHK-Cu — 50 mg copper-peptide vials; higher water volumes typical.
Full research peptide catalog

Frequently asked

How do I use a peptide reconstitution calculator?

Enter four values: the vial strength in milligrams (printed on the label), the volume of bacteriostatic water you plan to add, the target research dose in micrograms, and your syringe type. The calculator returns the peptide concentration (mcg/ml), the volume to draw (ml), and the equivalent mark on a U-100 insulin syringe in insulin units (IU).

What is an IU on an insulin syringe?

On a U-100 insulin syringe, "IU" refers to the unit markings on the barrel rather than an international unit of activity. 100 IU equals 1 ml, so 10 IU equals 0.10 ml. The calculator converts your draw volume to IU so you can read the correct mark directly on the syringe.

What syringe do I need for peptide research?

Most lyophilized research peptides are handled with U-100 insulin syringes. 1 ml (100 IU), 0.5 ml (50 IU), and 0.3 ml (30 IU) barrels are all U-100 — they measure the same concentration, just with finer graduations on smaller barrels. Pick the smallest barrel that still fits your draw so the marks are easier to read.

How much bacteriostatic water should I add to a peptide vial?

There is no single correct volume. Adding more water lowers concentration and makes small doses easier to measure; adding less keeps total injection volume small. Common laboratory choices are 1 ml, 2 ml, or 3 ml of bacteriostatic water per vial. The calculator accepts any volume and recomputes concentration on the fly.

How long does reconstituted peptide last?

Shelf life after reconstitution depends on the peptide, the solvent (bacteriostatic water contains 0.9% benzyl alcohol as a preservative), and storage temperature. As a general laboratory reference, reconstituted peptides are typically refrigerated at 2-8 degrees Celsius and used within a few weeks. Consult the certificate of analysis for the specific compound.

Is this calculator for human use?

No. This calculator is a laboratory reference tool. All peptides referenced on Capital Peptides are supplied for in-vitro research use only — not for human consumption, diagnostic, or therapeutic purposes. Consult qualified professionals for any clinical question.

Research Use Only. All products sold are for laboratory research purposes only. Not for human consumption, diagnostic use, or therapeutic use. Must be 21+ to purchase.