Arithmetic only — no dosing protocol
Peptide Reconstitution Calculator
Enter the milligrams on the vial and the millilitres of bacteriostatic water you added, and this converts a dose in micrograms into a mark on a U-100 insulin syringe.
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- Alpha Health Finder Editorial Team
- Last reviewed
Why the answer is in micrograms, and why this page names no dose
A lyophilised peptide vial is labelled with one number: a mass in milligrams. It has no concentration until a diluent goes in, and the volume you choose is what sets it. Concentration in mg/mL is the milligrams in the vial divided by the millilitres added — a 5 mg vial in 2 mL is 2.5 mg/mL, the same vial in 1 mL is 5 mg/mL. Nothing about the powder changes; only the size of the draw does.
The step that goes wrong is the next one, and it is not the U-100 conversion. Peptide doses are quoted in micrograms — 100 mcg, 250 mcg, 500 mcg — while the vial is labelled in milligrams. There are 1000 micrograms in a milligram, so someone who reads a 250 mcg dose as 250 mg is not slightly out, they are out by a factor of a thousand and there is not enough drug in the vial to make the error visible. Working the whole calculation in micrograms, as this page does, keeps that factor in one place instead of scattered through the arithmetic.
A U-100 insulin syringe is graduated so that 100 units is exactly 1 mL. That is not a clinical finding to be cited, it is what U-100 means — the definition of the barrel. So one unit mark is 0.01 mL, and at 2.5 mg/mL one unit mark carries 25 micrograms. This calculator rounds to the quarter unit and then shows you what that mark actually delivers, rather than echoing the dose you typed. A quarter unit is not a printed line: no barrel we could find a specification for is graduated that finely. It is the finest split anyone can reasonably judge between two lines, which is a weaker claim than a graduation and the only one the evidence supports.
This page will not tell you how much of anything to take. For most of the compounds people arrive here holding there is no sourceable dose to publish: no approved label, no dose-ranging trial, no regulator-reviewed instruction. FDA placed several of them — BPC-157, ipamorelin acetate, kisspeptin-10, KPV and pegylated mechano growth factor among others — in category 2 of its compounding bulks review, the list of bulk drug substances that in its assessment may present significant safety risks. Of BPC-157 it wrote: "FDA has identified no, or only limited, safety-related information for the proposed routes of administration. Therefore, the agency lacks sufficient information to know whether the drug would cause harm when administered to humans." When the regulator says it does not know, a directory publishing a milligram figure would be making one up. Arithmetic we can stand behind; a protocol we cannot.
A licensed peptide shows what a real reconstitution instruction looks like, and it is worth reading once. EGRIFTA WR is tesamorelin, a growth-hormone-releasing factor analogue, supplied as an 11.6 mg lyophilised vial with bacteriostatic water as the diluent. Its FDA label says: "Reconstitute 1 vial of EGRIFTA WR lyophilized powder with 1.3 mL of diluent (8 mg per mL)." and "One dose of EGRIFTA WR is 1.28 mg in 0.16 mL of the reconstituted solution." Note two things. The label states 8 mg/mL rather than the 8.92 mg/mL that 11.6 ÷ 1.3 would give, because the vial is deliberately overfilled and the labelled figure is what is reliably deliverable. And its Instructions for Use send the patient to "the 16 mark (0.16 mL)" — an FDA label doing exactly the mL-to-units conversion below. Where a manufacturer prints a concentration, use the manufacturer's, not this calculator's.
If your question is the other one — not "what do I draw" but "how much water should I add to land on a convenient mark" — the bacteriostatic water calculator solves for the diluent volume instead, and covers the benzyl alcohol content and the neonatal contraindication that come with it.
The formula
concentration (mg/mL) = vial contents (mg) ÷ diluent added (mL)
mcg per unit mark = concentration (mg/mL) × 1000 ÷ 100
units to draw = dose (mcg) ÷ mcg per unit mark
dose volume (mL) = units ÷ 100
doses per vial = vial contents (mg) × 1000 ÷ dose (mcg)
The 1000 is micrograms per milligram; the 100 is units per millilitre on a U-100 barrel. The powder’s own displaced volume is ignored, as manufacturers’ reconstitution tables do — for a few milligrams of lyophilised solid it sits below the resolution of the syringe reading the result. Units are rounded to the quarter mark because that is as finely as a barrel can be read; doses per vial is floored, because a part dose is not a dose, and it does not depend on the diluent at all.
Worked example
5 mg vial, reconstituted with 2 mL of bacteriostatic water, drawing a 250 mcg dose:
- Concentration = 5 mg ÷ 2 mL = 2.5 mg/mL
- One unit mark = 2.5 mg/mL × 1000 ÷ 100 = 25 mcg
- Units to draw = 250 mcg ÷ 25 mcg = 10 units
- Dose volume = 10 ÷ 100 = 0.1 mL
- The mark delivers 250 mcg — exact, because 250 is a whole number of 25s
- Doses per vial = 5000 mcg ÷ 250 mcg = 20 doses
- Same vial in 1 mL instead: 50 mcg a mark, so the same 250 mcg is 5 units — still 20 doses in the vial
Peptide reconstitution chart — micrograms per unit mark
What one unit on a U-100 insulin syringe delivers once the vial is mixed. Read down for the milligrams printed on your vial, across for the diluent you added.
| Vial | 1 mL diluent | 2 mL diluent | 3 mL diluent | 5 mL diluent |
|---|---|---|---|---|
| 2 mg2000 mcg total | 20 mcg2 mg/mL | 10 mcg1 mg/mL | 6.67 mcg0.667 mg/mL | 4 mcg0.4 mg/mL |
| 5 mg5000 mcg total | 50 mcg5 mg/mL | 25 mcg2.5 mg/mL | 16.67 mcg1.667 mg/mL | 10 mcg1 mg/mL |
| 10 mg10000 mcg total | 100 mcg10 mg/mL | 50 mcg5 mg/mL | 33.33 mcg3.333 mg/mL | 20 mcg2 mg/mL |
| 15 mg15000 mcg total | 150 mcg15 mg/mL | 75 mcg7.5 mg/mL | 50 mcg5 mg/mL | 30 mcg3 mg/mL |
| 20 mg20000 mcg total | 200 mcg20 mg/mL | 100 mcg10 mg/mL | 66.67 mcg6.667 mg/mL | 40 mcg4 mg/mL |
| 30 mg30000 mcg total | 300 mcg30 mg/mL | 150 mcg15 mg/mL | 100 mcg10 mg/mL | 60 mcg6 mg/mL |
This is the only number you need to keep. Once you know what a mark is worth in micrograms, every dose is one division. Every cell is computed by the same function the calculator above calls.
Units to draw for a dose in micrograms
Read down for your dose in mcg, across for what you actually mixed. The figure is units on a U-100 insulin syringe, rounded to the quarter mark a barrel can be read to.
| Dose | 2 mg + 1 mL20 mcg/unit | 5 mg + 2 mL25 mcg/unit | 5 mg + 1 mL50 mcg/unit | 15 mg + 2 mL75 mcg/unit | 10 mg + 1 mL100 mcg/unit |
|---|---|---|---|---|---|
| 100 mcg0.1 mg | 5 units0.05 mL | 4 units0.04 mL | 2 units0.02 mL | 1.25 units0.0125 mL → 93.75 mcg | 1 unit0.01 mL |
| 200 mcg0.2 mg | 10 units0.1 mL | 8 units0.08 mL | 4 units0.04 mL | 2.75 units0.0275 mL → 206.25 mcg | 2 units0.02 mL |
| 250 mcg0.25 mg | 12.5 units0.125 mL | 10 units0.1 mL | 5 units0.05 mL | 3.25 units0.0325 mL → 243.75 mcg | 2.5 units0.025 mL |
| 500 mcg0.5 mg | 25 units0.25 mL | 20 units0.2 mL | 10 units0.1 mL | 6.75 units0.0675 mL → 506.25 mcg | 5 units0.05 mL |
| 750 mcg0.75 mg | 37.5 units0.375 mL | 30 units0.3 mL | 15 units0.15 mL | 10 units0.1 mL | 7.5 units0.075 mL |
| 1000 mcg1 mg | 50 units0.5 mL | 40 units0.4 mL | 20 units0.2 mL | 13.25 units0.1325 mL → 993.75 mcg | 10 units0.1 mL |
| 2000 mcg2 mg | 100 units1 mL | 80 units0.8 mL | 40 units0.4 mL | 26.75 units0.2675 mL → 2006.25 mcg | 20 units0.2 mL |
Where the lower line shows a second microgram figure, the dose does not land on a mark: that is what the reachable quarter-unit actually delivers. A 250 mcg dose from a 15 mg vial in 2 mL is 3.333 units in theory, 3.25 units on the barrel, and 243.75 mcg in the syringe. More diluent makes the mark bigger and the rounding error smaller.
Doses per vial, and what is left over
Whole doses in each vial and the micrograms stranded after the last one. The diluent volume does not appear, because diluting further does not create more peptide.
| Vial | 100 mcg dose | 250 mcg dose | 500 mcg dose | 1000 mcg dose | 2000 mcg dose |
|---|---|---|---|---|---|
| 2 mg | 20 dosesnothing left | 8 dosesnothing left | 4 dosesnothing left | 2 dosesnothing left | 1 dosenothing left |
| 5 mg | 50 dosesnothing left | 20 dosesnothing left | 10 dosesnothing left | 5 dosesnothing left | 2 doses1000 mcg left |
| 10 mg | 100 dosesnothing left | 40 dosesnothing left | 20 dosesnothing left | 10 dosesnothing left | 5 dosesnothing left |
| 15 mg | 150 dosesnothing left | 60 dosesnothing left | 30 dosesnothing left | 15 dosesnothing left | 7 doses1000 mcg left |
| 20 mg | 200 dosesnothing left | 80 dosesnothing left | 40 dosesnothing left | 20 dosesnothing left | 10 dosesnothing left |
| 30 mg | 300 dosesnothing left | 120 dosesnothing left | 60 dosesnothing left | 30 dosesnothing left | 15 dosesnothing left |
Part doses are not counted. How long that many doses lasts depends on a dosing frequency this page does not supply, and on the beyond-use date of the reconstituted solution, which belongs to the compound and not to the water.
Frequently asked questions
- How do I calculate units for a peptide dose in mcg?
- Divide the milligrams in the vial by the millilitres of diluent to get mg/mL, multiply by 1000 to get mcg/mL, then divide by 100 because a U-100 syringe is 100 units per mL — that gives micrograms per unit mark. Your dose in mcg divided by that figure is the number of units. A 5 mg vial in 2 mL is 2.5 mg/mL, which is 25 mcg a mark, so a 250 mcg dose is 10 units and a 500 mcg dose is 20 units.
- How many mcg are in a mg of peptide?
- Exactly 1000. A 5 mg vial holds 5000 mcg, a 10 mg vial holds 10,000 mcg, a 2 mg vial holds 2000 mcg. This is the conversion that causes real harm when it slips: a 250 mcg dose is 0.25 mg, and anyone drawing 250 mg instead would be attempting fifty times the entire contents of a 5 mg vial. Work the whole calculation in one unit and convert once, at the start.
- How much of this peptide should I inject?
- This page will not answer that, and the honest reason is that there is no sourceable answer for most of these compounds. They have no approved label, no dose-ranging study and no regulator-reviewed instruction — FDA placed BPC-157, ipamorelin acetate, kisspeptin-10, KPV and others in category 2 of its compounding bulks review, and said of BPC-157 that it "lacks sufficient information to know whether the drug would cause harm when administered to humans". A number invented to fill that gap would look exactly like a real one. Ask a clinician who can see your history; this tool only converts the number you were given.
- Does adding more bacteriostatic water make the vial last longer?
- No. A 5 mg vial holds 5000 mcg whether you reconstitute it with 1 mL or 5 mL, so it contains twenty 250 mcg doses either way. What changes is the size of the draw. At 1 mL the vial is 5 mg/mL, 50 mcg a mark, and 250 mcg is 5 units; at 2 mL it is 25 mcg a mark and the same dose is 10 units; at 5 mL it is 10 mcg a mark and 25 units. More diluent buys a bigger, easier-to-read mark, not more drug.
- What if my dose does not land on a syringe mark?
- Then draw the nearest quarter unit and know what it delivers. A quarter unit is the finest split anyone can judge by eye between two printed lines — it is not itself a line on any barrel — so a 250 mcg dose from a 15 mg vial in 2 mL — 75 mcg a mark — is 3.33 units in theory, 3.25 units in practice, and 243.75 mcg in the syringe, about 2.5% short. Reconstituting the same vial with 3 mL instead gives 50 mcg a mark and puts the dose on exactly 5 units. Choosing a diluent volume that makes your dose a whole number of units is the fix.
- How long does bacteriostatic water last after the first puncture?
- The bacteriostatic water label itself does not state a period — a fact worth knowing, because the 28-day figure circulates as if it came from the bottle. It comes from two other places. CDC, citing USP General Chapter 797, states that "Once a multi-dose vial is opened (e.g., needle-punctured) the vial should be dated and discarded within 28 days unless the manufacturer states another date for that opened vial." And the EGRIFTA WR label, which supplies bacteriostatic water as its diluent, instructs patients to "Throw away (discard) any Bacteriostatic Water for Injection left in the bottle 28 days after first use." Date the vial at first puncture.
- How long does the reconstituted peptide keep?
- That is set by the compound, not by the diluent, and for an unapproved peptide nobody has established it. The bacteriostatic water label is explicit that you should "Do not store reconstituted solutions of drugs for injection unless otherwise directed by the manufacturer of the solute" — the water defers to the drug. Where a manufacturer has done the work the figure is specific and short: EGRIFTA WR, reconstituted, is discarded 7 days after mixing. With no label there is no number, and a forum consensus is not one.
- Why is the concentration on my vial different from this calculator?
- Because a manufacturer accounts for overfill and this calculator uses the nominal mass you typed. EGRIFTA WR is an 11.6 mg vial reconstituted with 1.3 mL, which divides out to 8.92 mg/mL, but the label states 8 mg/mL and a dose of 1.28 mg in 0.16 mL — the vial is overfilled so that the stated concentration is reliably deliverable. If your product came with a printed reconstitution table, that table wins. This tool is for the case where the vial arrived with nothing but a milligram figure on it.
- What size syringe should I use for a peptide dose?
- The smallest insulin barrel the draw fits in, because a given number of units occupies more of a small barrel and is therefore easier to read on it — a 10-unit draw is a third of a 30-unit barrel and a tenth of a 100-unit one. Barrels are commonly described as marked every 1 unit at 0.3 and 0.5 mL and every 2 units at 1 mL, but we could not source those intervals from any manufacturer instruction-for-use or FDA device listing, so this page does not state them as fact: count the lines between two numbers on your own barrel. Anything over 100 units is more than 1 mL and no insulin syringe holds it; use a stronger concentration rather than splitting the injection.
Sources
- [1]Bacteriostatic Water for Injection, USP — FDA prescribing information (Hospira, Inc.), DailyMed. "Bacteriostatic Water for Injection, USP is a sterile, nonpyrogenic preparation of water for injection containing 0.9% (9 mg/mL) or 1.1% (11 mg/mL) of benzyl alcohol added as a bacteriostatic preservative." and "Do not store reconstituted solutions of drugs for injection unless otherwise directed by the manufacturer of the solute."
- [2]EGRIFTA WR (tesamorelin) for injection — FDA prescribing information (Theratechnologies Inc.), DailyMed. A licensed lyophilised peptide reconstituted with bacteriostatic water: "Reconstitute 1 vial of EGRIFTA WR lyophilized powder with 1.3 mL of diluent (8 mg per mL)." and "One dose of EGRIFTA WR is 1.28 mg in 0.16 mL of the reconstituted solution." and "Throw away (discard) any Bacteriostatic Water for Injection left in the bottle 28 days after first use."
- [3]Centers for Disease Control and Prevention, Injection Safety — Clinical Safety Considerations. Citing USP General Chapter 797: "Once a multi-dose vial is opened (e.g., needle-punctured) the vial should be dated and discarded within 28 days unless the manufacturer states another date for that opened vial."
- [4]U.S. Food and Drug Administration — Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks (category 2). On BPC-157: "FDA has identified no, or only limited, safety-related information for the proposed routes of administration. Therefore, the agency lacks sufficient information to know whether the drug would cause harm when administered to humans."
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Educational reference, not medical advice. Unit conversion only. This tool does not recommend a dose, a frequency or a cycle for any peptide, and for most of these compounds no sourceable dose exists — no approved label, no dose-ranging trial. Reconstitution, storage and whether to inject anything at all belong to a prescribing clinician.