Peptide Reconstitution Calculator
Enter your vial size, how much bacteriostatic water you added, and the dose you're working with. The tool converts it into millilitres and insulin-syringe units — and shows you where that lands on the syringe.
This calculator performs a unit conversion on numbers you supply. It does not recommend a dose, and it cannot tell you what dose is appropriate for you — that is a question for a qualified healthcare professional. Example values are pre-filled purely to show how the tool works.
Three inputs, and the maths is done. All results assume a standard U-100 insulin syringe, where 1 ml equals 100 units.
The figure printed on the vial label, before you add anything.
Capped at 3 ml, because that is the capacity of a standard peptide vial. More on why below.
Whatever dose you have already established with a healthcare professional. This field is a conversion input, not a suggestion.
0.100 ml on a U-100 insulin syringe
This tool converts numbers. It does not verify that a dose is safe or appropriate, and it cannot account for your medical history, medications or condition. Check every result against the vial label before drawing anything.
How the Maths Works
There is no trick to it, and it is worth understanding rather than trusting a box on a screen. Three steps.
| Step | Calculation | Worked example |
|---|---|---|
| 1. Concentration | mg in the vial ÷ ml of bacteriostatic water | 10 mg ÷ 2 ml = 5 mg per ml |
| 2. Volume | dose ÷ concentration | 0.25 mg ÷ 5 mg/ml = 0.05 ml |
| 3. Units | volume in ml × 100 | 0.05 ml × 100 = 5 units |
The only conversion people trip over is between micrograms and milligrams: 1,000 mcg = 1 mg. A dose written as 250 mcg is 0.25 mg. Getting that one wrong by a factor of ten is the single most common error in this whole process, which is why the calculator above makes you pick the unit explicitly rather than guessing.
Units are not millilitres
On a U-100 insulin syringe, 100 units is 1 ml. So 50 units is 0.5 ml, and 10 units is 0.1 ml. The syringe is marked in units because that is how insulin is dosed, and the numbers printed on the barrel have nothing to do with milligrams of peptide. Two people using the same vial with different amounts of water will draw to completely different marks for the same dose.
Why 1–3 ml, and Not More
Search for reconstitution advice and you will find protocols calling for 4 ml, 5 ml, even 10 ml of bacteriostatic water. Take a 20 mg vial with a suggested 4 ml as the standard example. The arithmetic is fine. The physical instruction is not.
A standard peptide vial holds 3 ml. You cannot put 4 ml into it. To follow that instruction you would have to transfer the reconstituted solution into a separate sterile container — which means an extra transfer step, an extra opportunity for contamination, an extra piece of equipment, and no benefit whatsoever at the end of it.
1 to 3 ml covers every practical case
Across the vial sizes actually sold — 5 mg through 40 mg — and across any dose you are likely to be measuring, somewhere between 1 ml and 3 ml will put you in a readable range on an insulin syringe. There is no situation where going above 3 ml solves a problem that adjusting within that range could not. If a calculator tells you to add 5 ml, it is doing arithmetic without knowing what a vial looks like.
One further note at the top of the range: filling a 3 ml vial with a full 3 ml leaves no headroom, which makes pressure equalisation awkward when you draw. In practice 2 ml is the comfortable general-purpose default, with 3 ml as the working ceiling rather than a target.
Choosing Your Volume
Within that range, the trade-off is simple: more water means a bigger draw for the same dose, which is easier to measure accurately but a larger volume going under the skin.
| Volume | What it gives you | Suits |
|---|---|---|
| 1 ml | Most concentrated. Smallest injection volume, but small doses land on very few units and become hard to measure precisely | Larger doses, or where injection volume matters to you |
| 2 ml | The sensible default. Lands most vial-and-dose combinations somewhere readable, with headroom left in the vial | Most situations |
| 3 ml | Most dilute. Small doses spread across more units, so each mark is easier to hit — at the cost of a bigger draw and a completely full vial | Very small doses, or when precision matters most |
A practical target: aim for a draw somewhere between roughly 10 and 50 units. Below about 5 units you are measuring on a handful of marks and small errors become proportionally large. Above 100 units you have exceeded a single syringe. The calculator flags both.
Reading an Insulin Syringe
Most confusion here comes from the syringe rather than the maths.
- U-100 is the standard. The barrel is marked 0 to 100 units, and 100 units is exactly 1 ml. Every result from the calculator above assumes this.
- Barrel sizes vary, the scale does not. A 0.3 ml syringe reads 0 to 30 units, a 0.5 ml reads 0 to 50, a 1 ml reads 0 to 100. A unit is the same volume on all three — the smaller barrels simply have the marks further apart, which makes small draws easier to read.
- Read at the plunger's leading edge, at eye level, with the syringe held vertically.
- Clear the air. Bubbles occupy volume that should be solution. Tap them to the top and expel them before checking your mark.
For the full mixing procedure — aiming the water at the vial wall, swirling rather than shaking, wiping the stopper — see our guides on how to reconstitute peptides and dosing and injection basics.
Common Mistakes
Confusing mcg and mg
The ten-fold and hundred-fold errors nearly all start here. 1,000 mcg is 1 mg. Say the unit out loud when you set it.
Reading units as millilitres
"0.2 ml" is 20 units, not 2. The syringe scale and the calculator output are in different currencies.
Recalculating from memory
Change the water volume and every number changes. Redo the maths for each new vial rather than reusing last month's mark.
Not writing it down
Mark the vial with the date and the volume you added. A vial with unknown dilution is a vial you cannot dose from.
On storage: bacteriostatic water carries a 28-day in-use window from first puncture, and reconstituted solution stays refrigerated. Our page on storing peptides in tropical climates covers why that is less forgiving here than elsewhere, and how to minimize peptide side effects covers the handling habits that prevent most problems.
Common Questions
Does the amount of water change my dose?
No — and this is the point people find least intuitive. The dose is the amount of peptide, which is fixed by the vial. Water only changes how much liquid that peptide is spread through, and therefore how far along the syringe you draw. Same dose, different mark.
Why does your calculator stop at 3 ml?
Because a standard peptide vial holds 3 ml, and a calculator that produces physically impossible instructions is not doing you a favour. Anything above that requires transferring to a separate sterile container, which adds steps and contamination risk for no gain.
What if my result is under 5 units?
You are measuring on very few marks, so a small misread becomes a large proportional error. Using more bacteriostatic water within the 1–3 ml range spreads the same dose across more units and makes it easier to hit accurately. The calculator flags this automatically.
What if it comes out over 100 units?
That exceeds a single U-100 syringe. Using less water raises the concentration and brings the draw back within range. If it still will not fit at 1 ml, the dose is large relative to the vial size and worth re-checking with whoever set it.
Can I use sterile water instead?
Only for a single use. Sterile water has no preservative, so a vial reconstituted with it has no protection against bacterial growth between draws. Bacteriostatic water contains 0.9% benzyl alcohol, which is what makes repeated entry into the same vial reasonable.
How many doses will a vial give me?
Divide the vial's milligrams by your dose in milligrams — the calculator shows this. It is an arithmetic maximum rather than a promise: residual volume in the vial, dead space in the syringe and the 28-day in-use window all mean you may not extract every theoretical dose.
Does this work for any peptide?
The arithmetic is identical for anything supplied as a lyophilized powder measured in milligrams — the maths does not know or care which compound is in the vial. What differs between compounds is the appropriate dose, which is not something this tool addresses.
Where do I get bacteriostatic water?
It is available through us — see the BAC water page — and insulin syringes and alcohol swabs are widely available from pharmacies in Costa Rica. Message us if you are unsure what you need for a particular vial size.
Not sure your numbers are right?
Send us your vial size and what you're working with and we'll check the maths with you. We'd rather spend two minutes on that than have you guess.
Contact Us on WhatsAppImportant disclaimer: This calculator is a unit-conversion tool provided for general educational purposes. It is not medical advice, a prescription, or a dosing recommendation, and it does not suggest, endorse or validate any dose. It converts figures that you enter into a volume and a syringe reading; it cannot assess whether the dose you entered is safe, appropriate, or correct for you, and it takes no account of your medical history, existing conditions or other medications. The example values pre-filled in the tool exist solely to demonstrate its operation and are not recommendations. All results should be checked against the vial label and confirmed independently before any material is drawn or administered. Calculations assume a standard U-100 insulin syringe on which 100 units equals 1 millilitre; syringes calibrated to other standards will give different readings. The 3 ml ceiling reflects the physical capacity of standard peptide vials. Most peptides sold by Peptides Costa Rica are not approved by the FDA, the EMA, or Costa Rica's Ministerio de Salud as finished pharmaceutical drugs for human use and are sold as research compounds intended for laboratory and scientific study. Reconstituted solutions require refrigerated storage, and bacteriostatic water carries a 28-day in-use period from first puncture. Always consult a qualified healthcare professional before beginning or adjusting any peptide protocol. Products sold by Peptides Costa Rica are intended for laboratory and research purposes only.
- United States Pharmacopeia monographs and manufacturer datasheets: Composition of bacteriostatic water for injection, including 0.9% benzyl alcohol as preservative, and the 28-day in-use period following first puncture of a multi-dose vial.
- Insulin syringe manufacturer specifications: U-100 calibration, on which 100 units corresponds to 1 millilitre, and the 0.3 ml, 0.5 ml and 1 ml barrel sizes reading to 30, 50 and 100 units respectively.
- Published injection technique consensus recommendations: Guidance on air removal, vial stopper disinfection and handling of multi-dose vials.
- Lyophilized peptide vial specifications: Standard 3 ml vial capacity for research peptide presentations, which sets the practical ceiling on reconstitution volume.
