IU Dosage Calculator
For compounds measured in International Units rather than milligrams. Enter your vial, your water and your dose — the tool converts biological activity into a mark on the syringe.
This calculator converts figures you supply into a volume and a syringe reading. It does not recommend a dose and cannot tell you what dose is appropriate for you — that is a question for a qualified healthcare professional. Example values are pre-filled only to show how the tool works.
Results assume a U-100 insulin syringe, where 100 units equals 1 ml. Choose your barrel size below and the scale adjusts.
Whatever is printed on the label, before you add anything.
Capped at 3 ml, the capacity of a standard vial. More on this below.
A dose already established with a healthcare professional. This is a conversion input, not a suggestion.
Only used when your vial and your dose are in different unit systems.
A unit is the same volume on all three. Smaller barrels simply space the marks further apart, which makes small draws easier to read.
0.2 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 or medications. Check every result against the vial label before drawing anything.
IU Is Not a Syringe Unit
This is the single most important thing on the page, and it causes more confusion than every other part of peptide arithmetic combined.
Both get called "units". They measure completely unrelated things.
| International Unit (IU) | Syringe unit | |
|---|---|---|
| What it measures | Biological activity — how much effect the substance produces | Volume — how much liquid is in the barrel |
| Fixed value? | Defined per substance against an international reference standard | Always 0.01 ml on a U-100 syringe, for anything |
| Printed where | On the vial label | On the syringe barrel |
| Changes with dilution? | No. The vial contains what it contains | Yes. Same dose, different water, different mark |
Why this matters more than it sounds
"Draw 2 IU" and "draw to the 2-unit mark" are not the same instruction, and following one when you meant the other can be off by a factor of ten or more. With a 10 IU vial in 1 ml of water, 2 IU sits at the 20-unit mark. Add 2 ml of water instead and the same 2 IU sits at the 40-unit mark. The IU never changed; only the volume it is dissolved in did. Any instruction expressed in syringe units is meaningless unless you also know how much water went into that particular vial.
How the Maths Works
Four steps, and the tool is only doing arithmetic you can check yourself.
| Step | Calculation | Worked example |
|---|---|---|
| 1. Put both in the same unit | Convert mg to IU using the conversion rate, if needed | Vial already 10 IU; dose already 2 IU |
| 2. Concentration | IU in the vial ÷ ml of water | 10 IU ÷ 1 ml = 10 IU per ml |
| 3. Volume | dose ÷ concentration | 2 IU ÷ 10 IU/ml = 0.2 ml |
| 4. Syringe units | volume in ml × 100 | 0.2 × 100 = 20 units |
A second example with mixed units, since that is where the conversion rate earns its place. A 10 IU vial in 2 ml of water, with a dose written as 100 mcg. Convert the dose: 100 mcg is 0.1 mg, and at 3 IU per mg that is 0.3 IU. Concentration is 5 IU per ml. Volume is 0.3 ÷ 5 = 0.06 ml, which is 6 units.
The Conversion Rate
The conversion field only matters when your vial and your dose are written in different systems — a vial in IU and a dose in mcg, for instance. If both are in IU, the tool ignores it entirely.
For somatropin the standard is 1 mg = 3 IU. This comes from calibration against the World Health Organization reference preparation, and it is what approved product labels reflect — a 5 mg presentation is labelled 15 IU. It is the same across every brand, so a 10 IU vial holds roughly 3.33 mg and a 36 IU vial roughly 12 mg.
The rate is specific to the substance, not to peptides in general
There is no universal IU. Each conversion comes from a separate bioassay against a separate reference standard, which is why growth hormone sits at 3 IU per mg while human chorionic gonadotropin is somewhere around 9,000 to 10,000 IU per mg — three orders of magnitude apart. Applying one compound's rate to another produces a wildly wrong answer, and the tool will happily calculate it for you, because arithmetic has no idea what is in your vial. If your product's label states a potency, use that number rather than ours.
Two compounds we deliberately left out
Insulin. Published conversion factors disagree — figures between roughly 26 and 29 IU per mg circulate depending on which standard is cited. A miscalculated insulin dose can be fatal within hours, so this tool offers no insulin preset. Insulin dosing belongs with the prescriber and the pen or syringe supplied for it, not with a general-purpose calculator. hCG. The mass conversion is approximate and sources disagree, but it is also unnecessary: hCG is supplied and prescribed in IU, so there is no reason to convert it to milligrams at all. Enter the vial in IU and the dose in IU, and the conversion rate drops out of the calculation.
Which Compounds Use IU
Most research peptides are measured in milligrams and micrograms — for those, our reconstitution calculator is the better tool. IU labelling is the exception, and it is mostly historical: proteins were standardised by biological assay long before precise mass measurement was routine, and the convention stuck.
- Somatropin (HGH). Vials almost always labelled in IU — 4, 10, 12, 15 and 36 IU are common. See our page on somatropin and on peptides versus HGH.
- hCG. Supplied in large IU amounts, typically 5,000 or 10,000 IU per vial.
- Insulin. Dosed in IU, and outside the scope of this tool for the reason above.
- Some gonadotropins and erythropoietins. Also standardised by activity.
Worth noting what is not on that list: the growth hormone secretagogues. Sermorelin, ipamorelin, CJC-1295 and tesamorelin are all dosed in micrograms or milligrams, not IU, even though they act on the same axis. See how growth hormone peptides work for why they are a different class.
Choosing Your Water Volume
The same principle as any reconstitution: more water means a bigger draw for the same dose, which is easier to measure precisely but a larger volume under the skin.
The calculator caps at 3 ml because that is the capacity of a standard vial. Protocols calling for 5 ml are doing arithmetic without knowing what a vial looks like — following one means decanting into a separate sterile container, which adds a contamination risk and gains nothing.
For IU-labelled compounds specifically, 1 ml is the most common choice and it has a neat property: with a 10 IU vial in 1 ml, the concentration is 10 IU per ml, so 1 IU sits at exactly the 10-unit mark. That one-to-one tidiness is why 1 ml is conventional here, whereas 2 ml is the usual default for milligram-labelled peptides.
Which Syringe
All three common barrel sizes use the same U-100 scale — a unit is 0.01 ml on every one of them. The difference is how far apart the marks are printed.
| Barrel | Reads | Best for |
|---|---|---|
| 0.3 ml | 0 to 30 units | Small draws. The marks are widely spaced, so a few units are easy to hit accurately |
| 0.5 ml | 0 to 50 units | The general-purpose middle option |
| 1 ml | 0 to 100 units | Larger draws, or when one injection needs more than half a millilitre |
If your result comes out below about 5 units, a smaller barrel will make it considerably easier to measure than squinting at the bottom of a 1 ml syringe. If it comes out above your barrel's capacity, the tool flags it — either use a larger barrel or use less water.
Common Mistakes
Treating IU as a syringe unit
The error this whole page exists to prevent. "2 IU" is not "2 units" unless your concentration happens to make it so.
Borrowing someone else's mark
A forum post saying "draw to 15" is worthless without their vial size and water volume. Redo the maths for your own vial.
Using the wrong conversion rate
3 IU per mg applies to somatropin. Apply it to something else and the answer can be off by thousands of times.
Not labelling the vial
Change the water volume and every mark changes. Write the date and the volume on the vial, or you cannot dose from it later.
Our guides on reconstitution, dosing and injection basics and common beginner mistakes cover the practical side, and the peptide glossary defines any term here that is unfamiliar.
Common Questions
What actually is an International Unit?
A measure of biological activity, defined for each substance separately by comparing it against an international reference preparation in a standardised assay. It exists because two batches with identical mass can differ in potency, and for hormones the potency is what matters clinically.
How many mg is a 10 IU vial?
For somatropin, about 3.33 mg, since 1 mg is 3 IU. A 4 IU vial is roughly 1.33 mg, a 15 IU vial 5 mg and a 36 IU vial 12 mg. The calculator shows this conversion in the results panel.
Does adding more water reduce my dose?
No — this is the most persistent misconception in reconstitution. The vial contains a fixed amount of substance regardless of what you dissolve it in. More water means the same dose occupies more volume, so you draw to a higher mark. The dose is identical.
Why is 1 ml so common for IU vials?
Because it produces convenient numbers. A 10 IU vial in 1 ml gives 10 IU per ml, so 1 IU lands exactly on the 10-unit mark and 2 IU on the 20-unit mark. It is a convention of convenience rather than a rule, and any volume from 1 to 3 ml works fine.
Can I use this calculator for BPC-157 or other mg peptides?
You could by setting both fields to mg, but the reconstitution calculator is built for that and will be simpler. This one exists specifically for the IU layer.
Why doesn't the tool have an insulin preset?
Because published insulin conversion factors disagree with each other, and an insulin dosing error is dangerous in a way that a growth hormone error is not. Insulin should be dosed with the device and instructions supplied by the prescriber, not calculated on a website.
My label says a different potency. Which do I use?
Always the manufacturer's figure. The 3 IU per mg default is the accepted standard for somatropin, but if a product insert states its own potency, that number governs. The conversion field is editable for exactly this reason.
How should reconstituted solution be stored?
Refrigerated at 2–8°C, never frozen, and used within the in-use window — bacteriostatic water carries a 28-day limit from first puncture, and some products specify shorter. Our guide on storing peptides in tropical climates covers why this is less forgiving here than elsewhere.
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. Two minutes of our time beats a guess on yours.
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. The default conversion of 1 mg to 3 IU applies to somatropin and does not apply to other substances; International Unit definitions are substance-specific, derived from separate reference standards, and applying the wrong factor produces a materially incorrect result. Where a manufacturer states a potency for a specific product, that figure takes precedence. This tool provides no conversion factor for insulin, and insulin should only be dosed using the device and instructions provided by a prescriber. The 3 ml ceiling reflects the physical capacity of standard vials. Somatropin is a prescription medicine in most jurisdictions; 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 protocol. Products sold by Peptides Costa Rica are intended for laboratory and research purposes only.
- World Health Organization International Standards, maintained by the National Institute for Biological Standards and Control: Definition of the International Unit as a measure of biological activity established per substance against a reference preparation, and the basis for the somatropin potency standard.
- Approved somatropin product labelling: The conversion of 1 mg to 3 IU reflected consistently across recombinant human growth hormone presentations, including labels showing 5 mg as 15 IU.
- Clinical and pharmaceutical reference literature on unit conversion: Substance-specific IU-to-mass relationships, including the order-of-magnitude difference between somatropin and human chorionic gonadotropin, and the variation in published insulin conversion factors.
- 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.
- United States Pharmacopeia monographs and manufacturer datasheets: Composition of bacteriostatic water and the 28-day in-use period following first puncture of a multi-dose vial.
