Last reviewed: January 2026
Enter your vial, water volume, and dose — get the exact syringe line to draw to. Instantly.
The three inputs that drive everything:
The calculator divides your dose by the concentration to give you the exact volume to draw, then converts that to syringe units (IU).
This is the most common source of dangerous errors. 1 mg = 1,000 mcg. A 5 mg vial contains 5,000 mcg. If your protocol says "250 mcg," that equals 0.25 mg — a thousand times smaller than 250 mg. Never confuse these units. The calculator lets you toggle between them with a single tap so you can verify in both units.
On a standard U-100 insulin syringe (1 mL), there are 100 unit marks. Each mark = 0.01 mL. So "draw to 15 units" means you pull the plunger to the 15-unit line, which equals 0.15 mL. This is the standard for peptide administration. U-50 (0.5 mL) syringes have 50 marks, U-30 (0.3 mL) have 30 marks — the calculator adjusts the scale automatically.
Concentration (mcg/mL) = Vial total mcg ÷ mL of BAC water added.
Draw volume (mL) = Desired dose (mcg) ÷ Concentration (mcg/mL).
Syringe units (IU) = Draw volume (mL) × 100 (for a 1 mL syringe).
Example: 5 mg vial (5,000 mcg) + 2 mL BAC water = 2,500 mcg/mL concentration. For a 250 mcg dose: 250 ÷ 2,500 = 0.10 mL = 10 IU on a 100-unit syringe.
Most peptides are stable for 28–60 days refrigerated (2–8°C) after reconstitution. Keep away from light. Label each vial with the reconstitution date. Lyophilized (unmixed) peptides can be stored at -20°C for 12–24 months. Never refreeze after reconstituting — this degrades the peptide structure.
A peptide reconstitution calculator takes the size of your peptide vial (in mg), the volume of bacteriostatic water you plan to add (in mL), and the dose you want to draw (in mcg or mg) and returns exactly how many "units" to draw on a standard insulin syringe. The conversion sounds simple but combines three different units of measurement that are easy to confuse in real time at the kitchen counter — milligrams of peptide, milliliters of solution, and "units" on a U-100 insulin syringe (where 100 units equals 1 mL). Doing this math by hand under fatigue is the most common source of accidental dose errors, particularly when scaling protocols up or down.1
This calculator runs entirely in your browser — your inputs are not sent to any server, and no account is required. It supports BPC-157, TB-500, semaglutide, tirzepatide, retatrutide, CJC-1295 (with and without DAC), Ipamorelin, Sermorelin, IGF-1 LR3, GHK-Cu, melanotan II, epithalon, and 20+ other commonly-discussed research and clinical peptides. The math is identical across compounds; what differs is the typical dose range and the standard reconstitution volume that produces a comfortable syringe-draw size for that dose.
The core formula is: units to draw = (desired dose in mcg ÷ peptide concentration in mcg/mL) × 100. The concentration depends entirely on your reconstitution choice — a 5 mg vial diluted in 2 mL of bacteriostatic water yields 2,500 mcg/mL. To draw a 250 mcg dose at that concentration, you need 0.1 mL, which on a U-100 insulin syringe is 10 units. Drawing the same 250 mcg dose from a vial reconstituted in 5 mL (1,000 mcg/mL) instead requires 0.25 mL, or 25 units — much easier to measure precisely on the syringe scale.2
This trade-off is the most important reconstitution decision: more water means lower concentration, larger draws, and easier precision; less water means higher concentration, smaller draws, and longer vial life when doses are infrequent. The calculator helps you visualize this trade-off by showing what your specific dose looks like at different dilution choices.
| Peptide | Typical vial size | Common BAC water volume | Resulting concentration |
|---|---|---|---|
| BPC-157 | 5 mg | 2 mL | 2,500 mcg/mL |
| TB-500 | 5 mg | 2 mL | 2,500 mcg/mL |
| Semaglutide | 2 mg, 5 mg | 1–2 mL | 1,000–2,500 mcg/mL |
| Tirzepatide | 5 mg, 10 mg, 15 mg | 0.5–1.5 mL | ~10,000 mcg/mL |
| Retatrutide | 10 mg | 1–2 mL | 5,000–10,000 mcg/mL |
| CJC-1295 (no DAC) | 2 mg, 5 mg | 2 mL | 1,000–2,500 mcg/mL |
| CJC-1295 (with DAC) | 2 mg | 2 mL | 1,000 mcg/mL |
| Ipamorelin | 5 mg | 2 mL | 2,500 mcg/mL |
| Sermorelin | 5 mg, 10 mg | 2 mL | 2,500–5,000 mcg/mL |
| IGF-1 LR3 | 1 mg | 1 mL | 1,000 mcg/mL |
| GHK-Cu | 50 mg, 100 mg | 5 mL | 10,000–20,000 mcg/mL |
| Melanotan II | 10 mg | 2 mL | 5,000 mcg/mL |
| Epithalon | 10 mg, 50 mg | 2–5 mL | varies |
*Volumes shown are common starting points used in research and reported clinical practice. Your specific protocol should come from your physician or the source paper for your compound.
You have a 5 mg vial of BPC-157, and you plan to add 2 mL of bacteriostatic water. Your protocol calls for 250 mcg twice daily. Step by step:
If your protocol later changed to 500 mcg twice daily, the math becomes: 500 mcg ÷ 2,500 mcg/mL = 0.20 mL = 20 units. Same vial, same concentration, twice the draw. The calculator updates this on the fly so you don't have to redo the arithmetic each time you adjust a protocol.
Bacteriostatic water (BAC water) contains 0.9% benzyl alcohol, a preservative that suppresses bacterial growth in a multi-puncture-use vial. Sterile water for injection has no preservative — the vial is sterile when manufactured, but once punctured, contamination risk rises with every additional draw. For a peptide vial that will be punctured 20+ times over 2–4 weeks, BAC water is the standard choice and the one most published research stability data is based on. A reconstituted vial with BAC water is typically stable for 25–30 days refrigerated; with sterile water, the same vial should be discarded within 24–48 hours of first puncture even if mathematically more doses remain.3
Benzyl alcohol toxicity has been documented in neonates at sustained high doses, which is why BAC water is contraindicated in newborns. For adult research-peptide protocols at typical doses, the daily benzyl alcohol exposure is far below any concerning threshold — a 1 mL injection from a BAC-water-reconstituted vial contains roughly 9 mg of benzyl alcohol, well below the cumulative limits seen in neonatal IV scenarios.
Technique matters here. Mishandled reconstitution is one of the more common ways to physically damage a peptide before it ever reaches the injection site. The standard procedure:
Once reconstituted, store the vial in the main compartment of your refrigerator at 2–8 °C, on a middle shelf toward the back where temperature is most stable. Avoid the door (warmer, fluctuates) and the very back wall of some models (occasionally drops below freezing). For light-sensitive peptides — Ipamorelin, Sermorelin, semaglutide, tirzepatide — keep the vial in its original cardboard box or wrap in opaque film. Most reconstituted peptides remain stable for 25–30 days under proper storage; less stable compounds (IGF-1 LR3, CJC-1295 without DAC, epithalon) have shorter windows of 10–21 days. See our Peptide Storage Calculator for tracking expiry dates and remaining doses.
Critical rule: do not freeze a reconstituted vial. Freeze-thaw cycles create ice crystals that mechanically disrupt peptide structure, producing measurable activity loss even when each individual cycle is brief. Lyophilized (powder) peptide freezes well — that's how it's shipped — but once water is added, the vial stays in the refrigerator until empty.
Confusing mg with mcg. 1 mg = 1,000 mcg. A 250 mcg dose is one thousand times smaller than a 250 mg dose. Misreading a protocol can produce a 1,000× error in either direction. Always verify the unit symbol before drawing.
Using a U-40 syringe instead of U-100. Standard insulin syringes are U-100, where 100 units = 1 mL. U-40 syringes (used for some veterinary insulin) read differently — the same drawn volume corresponds to a different "unit" number. Verify that "U-100" is printed on your syringe before using.
Shaking the vial during reconstitution. Vigorous agitation produces foaming and shears peptide chains. Roll or gently swirl instead — full dissolution takes 30–60 seconds for most peptides, longer for some.
Reconstituting at too high a concentration for typical doses. If your protocol calls for 100 mcg doses and you reconstitute a 5 mg vial in 1 mL, your draw is 2 units — hard to measure precisely on the syringe scale. Diluting in 5 mL instead gives 10-unit draws, much easier to reproduce accurately.
Forgetting to factor reconstitution into dose math. The vial label says "5 mg" but you're injecting from a solution. Always work from concentration (mcg/mL) when computing volume, never from the raw vial size.