Peptide Reconstitution Calculator: mg/mL Concentration Chart by Vial Size and Water

How Do You Calculate Peptide Reconstitution Concentration?

Reconstitution concentration in mcg per mL equals vial size in mg multiplied by 1,000, divided by the mL of bacteriostatic water you add. A 5mg vial mixed with 2mL of water gives 2,500mcg/mL. That single number drives every dose you draw afterward.

This is the entire calculation a reconstitution calculator runs, and you can do it yourself with three inputs: the peptide amount printed on the vial in milligrams, the volume of bacteriostatic water you draw into the syringe before injecting it into the vial, and the target dose you plan to draw for a single research session, expressed in micrograms. Multiply the mg figure by 1,000 to convert it to mcg, divide by the water volume in mL to get your concentration, then divide your target dose by that concentration and multiply by 100 to get the units you draw on a standard U-100 insulin syringe. The tables below run that formula across the vial sizes and water volumes used most often in research settings, so you can check your own numbers, catch a mixing mistake before you draw a dose, or skip the arithmetic entirely and read the answer straight off the chart.

Peptide Reconstitution Concentration Chart: mg/mL by Vial Size and Water Volume

The table below shows the resulting concentration in mcg/mL for the three most common research peptide vial sizes (2mg, 5mg, 10mg) mixed with 1mL, 2mL, 3mL, or 5mL of bacteriostatic water. More water lowers the concentration; less water raises it.

These figures come directly from the formula above, not a lookup table someone copied from a forum. Run the numbers yourself and you will land on the same values every time.

Notice the pattern: doubling the water halves the concentration every time, because concentration is a straight division problem, not a curve. A 5mg vial in 1mL is exactly twice as concentrated as the same 5mg vial in 2mL. If you ever see a chart where doubling the water does not exactly halve the number, that chart is wrong.

How Many Units Do You Draw for a 250mcg or 500mcg Dose?

Once you know your concentration, units drawn equals your target dose in mcg divided by the concentration, multiplied by 100 (a U-100 syringe reads 100 units per mL). At 2,500mcg/mL, a 250mcg dose draws to 10 units; a 500mcg dose draws to 20 units.

The row that matters most is the 2mg vial mixed with 5mL of water: a 500mcg dose there draws to 125 units, which is more volume than a standard 1mL (100 unit) insulin syringe holds. That is not a syringe problem, it is a concentration problem: you diluted the vial past the point where your target dose fits in one draw. The fix is less water, not a bigger syringe.

Worked Example: Reconstituting a 5mg Vial for a 300mcg Research Dose

For a 5mg vial with 2mL of bacteriostatic water, concentration is 2,500mcg/mL. A 300mcg dose divided by 2,500mcg/mL, multiplied by 100, draws to 12 units on a U-100 syringe. That is the full calculation, start to finish.

Walk it through in three steps. First, convert the vial size to micrograms: 5mg times 1,000 equals 5,000mcg. Second, divide by the water volume: 5,000mcg divided by 2mL equals 2,500mcg/mL, your working concentration. Third, divide your target dose by that concentration and multiply by 100: 300 divided by 2,500 equals 0.12, times 100 equals 12 units. BPC-157 is a useful compound to anchor this example to because its own pharmacokinetics make the concentration step matter more than usual. A 2025 systematic review covering 544 articles and 36 studies found BPC-157 has a plasma half-life under 30 minutes, cleared through hepatic metabolism and renal excretion (Vasireddi et al. 2025). A compound clearing that fast rewards a dosing routine you can repeat exactly, session after session, which is the entire point of running the concentration math once and writing the result down rather than eyeballing a vial every time.

What Happens If You Add Too Much or Too Little Water?

Too much water dilutes the vial until your target dose requires drawing more volume than your syringe holds. Too little water concentrates the vial until a small dosing error becomes a large one, because each unit on the syringe now represents more mcg.

Neither mistake wastes the peptide itself, but both make the syringe harder to read accurately. A 0.3mL (30 unit) syringe has the finest gradations and is the right choice when your calculated draw is under 30 units; a 1mL (100 unit) syringe is easier to misread at low volumes because each small tick mark represents a larger swing in dose. If your calculated draw for a normal dose comes out under 5 units on a 1mL syringe, that is usually a sign to add less water next time so the same dose lands in a more readable range, typically 10 to 50 units.

How Do You Pick a Water Volume Before You Reconstitute?

Work backward from your syringe: decide the unit range you want a normal dose to land in (10 to 50 units reads most accurately), then solve for the water volume that puts your usual dose there, rather than picking a round water number first and hoping the units work out.

The back-solved formula is water in mL equals vial size in mg, times 10, times your target units, divided by your dose in mcg. For a 5mg vial where you want a 300mcg dose to land on exactly 20 units: 5 times 10 times 20, divided by 300, equals 3.3mL. Round to a water volume your syringe can measure precisely, generally the nearest 0.5mL, and recompute the resulting units before you draw your first real dose. Keep a note of the final concentration next to your research log; a mislabeled vial is the single most common source of a wrong dose, not the arithmetic itself. If you are sourcing the peptide itself, work only with a supplier that publishes independent third-party certificates of analysis, since a vial with an inaccurate mg fill invalidates every number in this article.

Frequently Asked Questions

Does the type of peptide change the reconstitution formula?

No. The mg-to-mcg-per-mL math is pure arithmetic and applies identically whether you are reconstituting BPC-157, TB-500, GHK-Cu, or any other lyophilised peptide. What changes between compounds is the target dose in mcg and the injection frequency, both of which come from research literature or your own protocol, not from the reconstitution formula.

What is bacteriostatic water and why not use sterile water?

Bacteriostatic water contains 0.9% benzyl alcohol as a preservative, which lets a reconstituted vial be drawn from multiple times over days or weeks without the water itself supporting bacterial growth. Sterile water with no preservative is intended for a single immediate use and is not appropriate for a vial you plan to store and redraw from.

How long does a reconstituted peptide vial stay usable?

Most compounding guidance for reconstituted peptides in bacteriostatic water points to a 2 to 4 week usable window under refrigeration, though the exact figure depends on the specific peptide's stability profile. Store the vial cold, away from light, and discard it past the window rather than testing whether it still works.

Can I use a different water volume than a chart recommends?

Yes. There is no single correct water volume for any vial size; the right volume is whichever one makes your specific target dose land on a syringe reading you can measure accurately. Use the back-solved formula in this article rather than defaulting to whatever volume a chart happens to list.

Why do my units not match a chart I found elsewhere?

Check three things in order: the vial size printed on your actual vial (not the size you intended to buy), the exact water volume you measured, and whether the chart you are comparing against assumes the same U-100 syringe standard (100 units per mL) this article uses. A mismatch in any one of those three throws every downstream number off.

Does temperature affect the concentration once reconstituted?

No. Concentration is a function of mass and volume, not temperature, so a correctly mixed vial has the same mcg/mL whether it is refrigerated or briefly at room temperature. Cold storage is about preserving the peptide's stability over time, not about maintaining the concentration figure itself.

References

• Vasireddi et al. 2025, "Emerging Use of BPC-157 in Orthopaedic Sports Medicine: A Systematic Review," HSS J. PubMed
• Seiwerth et al. 2021, "Stable Gastric Pentadecapeptide BPC 157 and Wound Healing," Front Pharmacol. PubMed
• Goldstein et al. 2011, "Thymosin β4: a multi-functional regenerative peptide," Expert Opin Biol Ther. PubMed
• Pickart et al. 2018, "Regenerative and Protective Actions of the GHK-Cu Peptide in the Light of the New Gene Data," Int J Mol Sci. PubMed

This content is for educational purposes only. These compounds are intended for research use. Nothing here is medical advice. Always work with a qualified clinician before making changes to your health protocol.

Related reading: for injection technique once you have drawn the correct dose, see our guide on how to inject peptides, and for a worked dosing example on a specific compound see the BPC-157 complete guide.