Peptide Calculator
Reconstitution concentration, syringe units, and per-dose volume — worked out from your vial size, bacteriostatic water, and target dose.
The total liquid volume you draw into the vial before mixing.
Draw to
—
units on your syringe
How the math works
Reconstitution just means turning a freeze-dried peptide back into a liquid you can measure with a syringe. Once you add bacteriostatic water, the peptide is evenly distributed through that liquid, so the concentration is fixed by two numbers: how much peptide is in the vial, and how much water you added.
volume to draw (mL) = desired dose (mg) ÷ concentration (mg/mL)
syringe units = volume to draw (mL) × syringe scale (100 for U-100, 40 for U-40)
Worked example
A 5 mg vial mixed with 2 mL of bacteriostatic water gives a concentration of 2.5 mg/mL. For a 250 mcg (0.25 mg) dose, you’d draw 0.1 mL — which reads as 10 units on a U-100 insulin syringe. That vial gives you roughly 20 doses before it’s empty.
Why the water volume matters more than people expect
Adding more bacteriostatic water doesn’t change the total amount of peptide in the vial — it changes how “spread out” it is. Less water means a stronger, more concentrated solution, so each dose is a smaller, harder-to-read volume. More water means a gentler concentration and an easier-to-measure draw, at the cost of using up the vial faster. Most people pick a water volume that lands their typical dose somewhere between 5 and 20 units, since that range is easiest to read accurately on a standard insulin syringe.
Common peptides & typical vial ranges
These are general reconstitution ranges people commonly use as a starting reference, not a prescription. GLP-1 style peptides like retatrutide are usually dosed on a weekly titration schedule rather than a flat daily amount, so if that’s what you’re working with, a dedicated retatrutide dosage calculator will walk through the titration steps in more detail than a general-purpose tool like this one can.
| Peptide | Typical vial size | Common water added | Resulting concentration |
|---|---|---|---|
| BPC-157 | 5 mg | 2–3 mL | 1.7–2.5 mg/mL |
| TB-500 | 5 mg | 2 mL | 2.5 mg/mL |
| Ipamorelin | 5 mg | 2 mL | 2.5 mg/mL |
| CJC-1295 | 2 mg | 2 mL | 1 mg/mL |
| Semaglutide | 5 mg | 2 mL | 2.5 mg/mL |
| Retatrutide | 10 mg | 2 mL | 5 mg/mL |
Frequently asked questions
Use the marking on your syringe barrel from when you drew the water — that’s your water volume in mL. If you’re estimating, round down slightly; a slightly more concentrated solution is easier to correct than the reverse.
Just how it’s displayed. The actual liquid volume you need doesn’t change — only the number printed next to the plunger does, because U-100 and U-40 syringes use different unit scales for the same 1 mL barrel.
That’s normal — it’s simply what the math produces for your specific vial size, water volume, and dose. Most insulin syringes are marked in single-unit increments, so you’d round to the nearest visible line your syringe supports.
No. It only performs the arithmetic of concentration and volume based on numbers you enter. It doesn’t evaluate whether a dose, peptide, or schedule is appropriate for you.
References
- U.S. Food & Drug Administration — Human Drug Compounding
- MedlinePlus (National Institutes of Health) — Giving a Subcutaneous Injection
- Centers for Disease Control and Prevention — Injection Safety
- United States Pharmacopeia — General Chapter <797>, Pharmaceutical Compounding: Sterile Preparations