Peptide Reconstitution Calculator — dose, draw volume & syringe units

Not medical advice. This tool does only the reconstitution arithmetic. It does not tell you whether to use any substance, which substance, what dose, or how often — and it makes no claim that any peptide is safe or effective. Use it only for a substance that has been lawfully prescribed or administered to you, and confirm every figure with the prescribing clinician or pharmacist before drawing or injecting anything. Reconstituted vials, dose, sterility and disposal all carry real risk; a calculator cannot manage that for you.

How it works

Reconstitution mixes a dry peptide with a liquid (usually bacteriostatic water) so you can measure small doses. The maths is the same dilution relationship used throughout chemistry — concentration is amount divided by volume.

• Concentration (mg/mL) = peptide amount (mg) ÷ water added (mL). More water makes a weaker, larger-volume solution; less water makes it stronger.
• Draw volume (mL) = dose ÷ concentration. Your dose is entered in micrograms (mcg); 1000 mcg = 1 mg, so a 250 mcg dose is 0.25 mg.
• Syringe units = draw volume × 100. A standard U-100 insulin syringe is marked so that 100 units = 1 mL — one unit is 0.01 mL. So 0.1 mL is 10 units. Always confirm your syringe is U-100; U-40 and U-500 syringes use different markings and would give the wrong amount. If the result is more than 100 units, the draw is larger than one full 1 mL syringe — re-check the dose and the mix.
• Doses per vial = peptide amount ÷ dose, rounded down to whole doses. How many full doses the vial yields before it runs out.

If a dose would need more liquid than the whole vial holds (i.e. the dose is larger than the peptide in the vial), the draw fields show "—" — that entry is out of range, so re-check the numbers. Nothing here changes the total amount of peptide — only how it is diluted. Diluting more does not give you more drug per dose; it just spreads the same amount across a larger volume.

Worked example

A 5 mg vial, reconstituted with 2 mL of bacteriostatic water, for a 250 mcg dose:

• Concentration = 5 mg ÷ 2 mL = 2.5 mg/mL
• Dose in mg = 250 mcg ÷ 1000 = 0.25 mg
• Draw volume = 0.25 mg ÷ 2.5 mg/mL = 0.1 mL
• Syringe units = 0.1 mL × 100 = 10 units on a U-100 syringe
• Doses per vial = 5 mg ÷ 0.25 mg = 20 doses

If you used 1 mL of water instead, the concentration doubles to 5 mg/mL and the same 250 mcg dose is only 0.05 mL — 5 units. The dose is identical; the volume is smaller because the solution is more concentrated.

Frequently asked questions

How much bacteriostatic water should I add?

Whatever your clinician or the product instructions specify. There is no single "correct" volume — more water simply makes a weaker solution that is easier to measure in larger units, while less water makes a stronger one. This calculator shows the result for whatever volume you enter; it does not recommend a volume.

What is a U-100 insulin syringe and why does it matter?

U-100 is the most common insulin syringe: it is calibrated so 100 units span exactly 1 mL, meaning 1 unit = 0.01 mL. The "units" here are volume marks on that syringe, not a dose of the peptide. If your syringe is not U-100 (some are U-40 or U-500), the unit marks mean different volumes and this figure would be wrong — check the barrel before drawing.

Is bacteriostatic water the same as sterile water?

No. They are different products with different uses, and which is appropriate depends on the substance and how often the vial is accessed. This is exactly the kind of choice to confirm with a pharmacist or clinician — it is outside what a calculator can decide.

Does adding more water give a bigger dose?

No. The vial contains a fixed amount of peptide. Adding more water only dilutes it — each dose then occupies a larger volume, but contains the same micrograms. To change the dose you change the dose, not the water.

Why is my draw volume a very small number?

Peptide doses are often tens or hundreds of micrograms, so the volume to draw is frequently well under 0.1 mL. That is why insulin syringes (with fine unit markings) are used to measure it. If the volume is too small to measure accurately, a more dilute mix (more water) spreads the same dose across more units.

Why is the dose entered in micrograms (mcg)?

Because many peptide doses are a fraction of a milligram, and micrograms keep the number readable — 250 mcg rather than 0.25 mg. The calculator converts internally (1,000 mcg = 1 mg) before working out the volume. If your dose is written in milligrams, multiply by 1,000 to enter it here.