HGH IU to mg Calculator

How to use the HGH calculator

The calculator has two modes. IU ↔ mg converts a single amount. Reconstitution takes a vial, the diluent and a prescribed dose and tells you what to draw. Your inputs stay in the page link, so you can bookmark or share an exact result.

1. Pick a mode. Use IU ↔ mg if you only need to translate a label or a prescription. Use Reconstitution if you are drawing from a vial with an insulin syringe.
2. Enter the strength from the label. Choose IU or mg to match what is printed. The line under the box shows the same amount in the other unit.
3. Enter the diluent. This is the volume of bacteriostatic water or supplied diluent in the vial, in mL. For a prefilled cartridge, enter its volume, such as 1.5 mL.
4. Enter the prescribed dose. Type it in IU or mg exactly as your prescriber wrote it. The calculator does not suggest a dose.
5. Choose the syringe and read the result. The large number is the U-100 mark to draw to. Below it are the volume, IU per mL, IU per unit and doses per vial. Open Show the math to check each step.

The HGH IU to mg formula

Converting somatropin is a single multiplication or division. The constant is 3, the number of international units assigned to each milligram.

If you need micrograms, multiply mg by 1,000. The mcg to mg converter covers every metric step between grams and nanograms.

Why 3 IU equals 1 mg

An international unit is not a unit of mass. It is a unit of biological activity, defined by a reference preparation that the World Health Organization (WHO) holds for each substance. The IU of vitamin D and the IU of somatropin have nothing to do with each other.

For somatropin, the reference is the 2nd WHO International Standard, NIBSC code 98/574. The WHO Expert Committee on Biological Standardization established it in 2001, when it replaced the 1st standard, 88/624. Each ampoule holds 1.95 mg of somatropin, and the standard is assigned 3.0 international units per mg.

NIBSC’s instructions for use explain that the standard’s value is assigned in mass, so manufacturers can set potency in milligrams with a chemical assay such as HPLC. They treat the IU as a historical unit, offered as an optional conversion. In other words, 3 IU per mg is a bookkeeping rule tied to one reference material. It is not a physical constant, and it only works when a product meets that standard.

Why US labels use mg and other labels use IU

Every US prescribing label we checked states somatropin strength in milligrams: Genotropin, Norditropin, Omnitrope, Saizen and Zomacton. Humatrope is the exception that prints both. Its label reads 6 mg (18 IU), 12 mg (36 IU) or 24 mg (72 IU), which is exactly 3 IU per mg.

Labels outside the US vary. The European Omnitrope product information prints 5 mg as 15 IU, 10 mg as 30 IU and 15 mg as 45 IU. The UK Norditropin summary of product characteristics states that 1 mg corresponds to 3 IU. The South African Genotropin label is named for its IU content, 16 IU (5.3 mg), and expresses its doses in IU per kg.

Rounding explains the small gaps: 5.3 mg × 3 is 15.9 IU, printed as 16 IU. The Institute for Safe Medication Practices (ISMP) lists the abbreviation IU as error-prone because it can be misread as IV or the number 10. When you write amounts down, spell out international units or use mg, so they never get confused with syringe units.

What somatropin is

Somatropin is recombinant human growth hormone (GH). The labels describe a protein of 191 amino acids with a molecular weight of about 22,125 daltons, roughly 22 kDa, and an amino acid sequence identical to growth hormone from the pituitary gland. Genotropin and Humatrope are made in Escherichia coli bacteria.

It works by binding growth hormone receptors on target cells. That triggers production of GH-dependent proteins, including insulin-like growth factor 1 (IGF-1). Some effects are direct and some run through IGF-1. At 191 amino acids, somatropin is a full protein rather than a short peptide, though it is often grouped with peptides and searched for as an HGH peptide calculator.

Labels report a half-life of about 3 to 4 hours after an injection under the skin: 3.0 hours for Genotropin in adults with GH deficiency and 3.8 hours for Humatrope. Intravenous somatropin clears much faster; the difference comes from slow absorption from the injection site. Label doses are weight-based (mg/kg) for specific indications and must be prescribed.

HGH vial and cartridge sizes in IU and mg

The table lists somatropin strengths from current product labels, with the IU equivalent at 3 IU per mg. The label strength is always the number to trust; the IU column is the conversion.

US strengths from the prescribing information for Genotropin, Humatrope, Norditropin, Omnitrope, Saizen and Zomacton. Genotropin also comes in single-dose MiniQuick strengths from 0.2 to 2 mg.

Going the other way, here are sizes you may see printed in IU, converted to mg and mcg:

From IU to syringe units

The diagram follows one vial from its label to a syringe reading. The IU and mg columns are two names for the same amount. The water is what turns an amount into a volume.

HGH reconstitution: how much water to add

Start with the label. Where a label gives a range, you still choose the exact volume within it, and that choice sets every unit count afterwards.

• Saizen: 1 to 3 mL of bacteriostatic water for the 5 mg vial, and 2 to 3 mL for the 8.8 mg vial.
• Zomacton: 1 to 5 mL of the supplied bacteriostatic sodium chloride for the 5 mg vial, and the supplied 1 mL syringe of diluent for the 10 mg vial.
• Omnitrope 5.8 mg vial: comes with a 1.14 mL vial of bacteriostatic water containing 1.5% benzyl alcohol.
• Genotropin and Humatrope: cartridges come with their own diluent. Genotropin mixes inside a two-chamber cartridge to 5 mg/mL or 12 mg/mL.
• Norditropin pens and Omnitrope cartridges: arrive as ready-made solutions, so no mixing is needed. Norditropin FlexPro pens dial the dose in mg, not syringe units.

For a vial you draw from with an insulin syringe, the chart gives the U-100 units that hold 1 IU. Multiply by the IU on your prescription. More water means more units for the same IU, which makes small doses easier to measure.

Example: a 12 IU vial with 2 mL gives 16.67 units per IU. To get the concentration, divide vial IU by water mL. The peptide reconstitution calculator does the same math in mg and mcg.

If you would rather pick a round number of units first and solve for the water, the BAC water calculator works backwards. For a mg or mL amount that you want to express in units, use the mg to units calculator.

Worked examples

Example 1: 10 IU vial, 1 mL of water, 2 IU prescribed

Concentration is 10 ÷ 1 = 10 IU/mL, or 3.33 mg/mL. Volume is 2 ÷ 10 = 0.2 mL, which is 20 units. Each unit holds 0.1 IU, and the vial holds 5 doses of that size.

Example 2: 24 IU vial, 2 mL of water, 3 IU prescribed

Concentration is 24 ÷ 2 = 12 IU/mL. Volume is 3 ÷ 12 = 0.25 mL, or 25 units. In mg, the vial is 8 mg and the dose is 1 mg, which gives the same answer. The vial holds 8 doses.

Example 3: an IU vial and a mg prescription

A vial labelled 30 IU is 10 mg. Mixed with 2 mL it holds 15 IU/mL, or 5 mg/mL. A prescription for 0.5 mg is 0.5 × 3 = 1.5 IU. Volume is 0.5 ÷ 5 = 0.1 mL, or 10 units. Converting both numbers into the same unit first avoids every mix-up.

Example 4: the water changed, the instructions did not

Suppose a plan says 1 IU is 20 units, which is right for a 10 IU vial mixed with 2 mL. If the vial is actually mixed with 1 mL, each unit now holds 0.1 IU. Drawing 20 units then delivers 2 IU, twice the plan. The correct draw is 10 units.

Example 5: reading IU as syringe units

A 10 IU vial mixed with 2 mL holds 5 IU/mL. A 2 IU dose is 40 units. Someone who draws 2 units because the prescription says 2 IU gets 0.1 IU, one twentieth of the dose. The calculator shows a warning whenever the IU and the unit count differ. To check what a given number of units contains, enter the vial in mg (IU ÷ 3) in the reverse peptide calculator, which turns units back into mg.

Storage per the labels

Every somatropin product has its own storage rules, and they differ more than you might expect. These come from the current US prescribing information. Keep somatropin away from light and never freeze it once mixed.

Knowing how long a vial lasts matters for planning. The doses per vial calculator shows whether you will finish a vial before its in-use limit.

Prescription status and anti-doping rules

Somatropin is a prescription drug in the US. Federal law goes further than for most prescription drugs: 21 U.S.C. 333(e) makes it a crime to distribute human growth hormone, or possess it with intent to distribute, for any use other than treating a disease or recognized medical condition that FDA has authorized, on a physician’s order. The penalty is up to 5 years in prison. The statute defines human growth hormone as somatrem, somatropin or an analogue of either.

In sport, the World Anti-Doping Agency (WADA) 2026 Prohibited List, in force since January 1, 2026, places growth hormone, its analogues and its fragments in class S2.2.3. The list names the long-acting analogues lonapegsomatropin, somapacitan and somatrogon, and the fragments AOD-9604 and hGH 176-191. Growth hormone releasing factors, such as sermorelin and tesamorelin, and secretagogues, such as ibutamoren and ipamorelin, fall under S2.2.4. All of them are prohibited at all times, in and out of competition.

Common HGH conversion mistakes

Most errors come from mixing up scales that sound alike. The calculator checks for each of these.

• Treating IU as syringe units. A 2 IU dose is 2 syringe units only at 100 IU per mL. The calculator warns whenever the two numbers differ.
• Changing the water without recalculating. Twice the water means twice the units for the same IU, as Example 4 shows.
• Mixing IU and mg in one sum. Convert the vial and the dose into the same unit before dividing. The calculator flags a vial above 30 mg, the largest strength in the table, as a possible IU typed as mg.
• Losing a factor of 1,000. 0.4 mg is 400 mcg, not 4 mcg. When in doubt, check with the mcg to mg converter.
• Expecting labels to match the math exactly. 5.3 mg is 15.9 IU, printed as 16 IU. Use the label value.
• Drawing tiny volumes. Under about 2 units, a small misreading is a large error. More water, or a 0.3 mL syringe, makes the draw easier to read.
• Assuming a pen works like a syringe. Pens such as Norditropin FlexPro dial the dose in mg. Do not convert a pen setting into syringe units.

Key terms

Somatropin

Recombinant human growth hormone: 191 amino acids, about 22 kDa, identical in sequence to pituitary GH.

International unit (IU)

A unit of biological activity defined by a WHO reference preparation. Each substance has its own IU.

International Standard

The reference material that defines a unit. For somatropin it is NIBSC 98/574, at 3.0 IU per mg.

Reconstitution

Adding diluent to a freeze-dried powder to make a solution of known strength.

Diluent

The liquid used for mixing, such as bacteriostatic water or the solution supplied with the product.

U-100 syringe

An insulin syringe marked in 100 units per mL, so 1 unit is 0.01 mL.

IGF-1

Insulin-like growth factor 1, a protein made in response to growth hormone that carries many of its effects.

Frequently asked questions

Sources

We check every formula and figure on this page against primary sources. See our editorial policy for how we review content.