OptiPin
IU to mL calculator
An international unit is a potency, not a volume. The diluent is what turns one into the other.
The short answer
An international unit is a measure of biological potency, not of volume or mass. A vial marked 5,000 IU tells you what is in the whole vial. It becomes a concentration only once you add diluent.
mL = dose in IU ÷ (vial IU ÷ mL of diluent added)
So a 5,000 IU vial with 1 mL of bacteriostatic water is 5,000 IU/mL. A 500 IU dose is 0.1 mL, which is 10 units on a U-100 syringe. Reconstitute the same vial with 5 mL and that 500 IU dose becomes 0.5 mL, or 50 units.
A question like "500 IU to mL" therefore has no answer until the diluent volume is known. It is the missing half of the question, not a detail.
Convert your IU
Runs entirely in your browser. Nothing is sent anywhere.
Which vials are labeled in IU
Two families of compound reach people in international units rather than milligrams. They behave differently once you start converting.
- hCG. Sold by potency, with no mass on the carton at all. The Fresenius Kabi chorionic gonadotropin label describes a 10 mL multiple-dose vial of 10,000 USP units supplied with its diluent. There is no milligram figure to convert to.
- Somatropin. Modern labels are in milligrams, but pens and vials are still widely discussed in IU. Here a conversion does exist, because the WHO standard the potency is calibrated against carries a specific activity.
For anything else measured in a syringe, check whether the number on the vial is a potency or a mass before you treat it as one. If it is a mass, the mg to units calculator is the right tool instead.
5,000 IU vial: dose to units
The most common hCG vial size. Find the column for the diluent you added, then read down to your dose. Units are on a U-100 syringe.
| Dose | + 1 mL 50 IU per unit | + 2 mL 25 IU per unit | + 3 mL 16.67 IU per unit | + 5 mL 10 IU per unit |
|---|---|---|---|---|
| 250 IU | 5 u 0.05 mL | 10 u 0.1 mL | 15 u 0.15 mL | 25 u 0.25 mL |
| 500 IU | 10 u 0.1 mL | 20 u 0.2 mL | 30 u 0.3 mL | 50 u 0.5 mL |
| 1,000 IU | 20 u 0.2 mL | 40 u 0.4 mL | 60 u 0.6 mL | 100 u 1 mL |
| 1,500 IU | 30 u 0.3 mL | 60 u 0.6 mL | 90 u 0.9 mL | 150 u 1.5 mL |
| 2,000 IU | 40 u 0.4 mL | 80 u 0.8 mL | 120 u 1.2 mL | 200 u 2 mL |
| 2,500 IU | 50 u 0.5 mL | 100 u 1 mL | 150 u 1.5 mL | 250 u 2.5 mL |
More diluent is not weaker medicine. It is the same total potency in a larger volume, so each unit carries less and small doses become easier to measure.
10,000 IU vial: dose to units
| Dose | + 1 mL 100 IU per unit | + 2 mL 50 IU per unit | + 3 mL 33.33 IU per unit | + 5 mL 20 IU per unit |
|---|---|---|---|---|
| 250 IU | 2.5 u 0.03 mL | 5 u 0.05 mL | 7.5 u 0.07 mL | 12.5 u 0.12 mL |
| 500 IU | 5 u 0.05 mL | 10 u 0.1 mL | 15 u 0.15 mL | 25 u 0.25 mL |
| 1,000 IU | 10 u 0.1 mL | 20 u 0.2 mL | 30 u 0.3 mL | 50 u 0.5 mL |
| 1,500 IU | 15 u 0.15 mL | 30 u 0.3 mL | 45 u 0.45 mL | 75 u 0.75 mL |
| 2,000 IU | 20 u 0.2 mL | 40 u 0.4 mL | 60 u 0.6 mL | 100 u 1 mL |
| 2,500 IU | 25 u 0.25 mL | 50 u 0.5 mL | 75 u 0.75 mL | 125 u 1.25 mL |
Doses under about 5 units sit at the limit of what a 1 mL barrel can be read to. A larger diluent volume, or a 0.3 mL syringe, fixes that.
IU to mg depends entirely on the hormone
There is no universal IU. The unit is defined separately for each substance against its own reference preparation, so a conversion factor for one hormone says nothing about another.
Somatropin (growth hormone)
The 2nd WHO International Standard for Somatropin, NIBSC code 98/574, is value-assigned in mass units at 1.95 mg per ampoule. Its instructions give 3.0 IU/mg for bioassay calibration. That is where the familiar "1 mg is 3 IU" comes from. The same document describes the IU as the historical unit, which is why current labels lead with milligrams.
| Somatropin | Equivalent mass |
|---|---|
| 1 IU | 0.33 mg |
| 2 IU | 0.67 mg |
| 3 IU | 1 mg |
| 4 IU | 1.33 mg |
| 5 IU | 1.67 mg |
| 6 IU | 2 mg |
| 8 IU | 2.67 mg |
| 10 IU | 3.33 mg |
| 12 IU | 4 mg |
| 15 IU | 5 mg |
| 30 IU | 10 mg |
| 36 IU | 12 mg |
At 3.0 IU/mg. A 36 IU pen is 12 mg, a 30 IU pen is 10 mg. Check your own carton rather than assuming, since it may state the milligram figure directly.
hCG
No equivalent conversion is printed. Urinary-derived and recombinant hCG are not even sold in the same system: the urinary product is labeled in USP units, while recombinant choriogonadotropin alfa is labeled by mass, at 250 mcg per pre-filled syringe. So asking how many milligrams are in 5,000 IU of hCG has no answer you can read off a label. Work in IU, which is what your vial, your protocol and your prescriber all use.
Check the barrel says U-100
Unit counts on this page are for a U-100 insulin syringe, where one unit is 0.01 mL. U-40 barrels, still sold for veterinary insulin, put one unit at 0.025 mL.
Confusing the two is especially easy here, because the syringe unit and the international unit are both called a unit while being entirely unrelated. One is a volume marking on a barrel. The other is a measure of biological activity.
If you realize after injecting that you drew substantially more than you intended, contact a clinician or your local poison control service rather than waiting to see how it goes. Bring the vial and its concentration with you.
Frequently asked questions
How many mL is 500 IU?
It depends on how the vial was reconstituted. A 5,000 IU vial with 1 mL of diluent is 5,000 IU/mL, so 500 IU is 0.1 mL, which is 10 units on a U-100 syringe. The same vial with 2 mL of diluent makes 500 IU into 0.2 mL, or 20 units. The vial strength and the diluent volume are both required.
How many mL is 5,000 IU?
If a 5,000 IU vial was reconstituted with 1 mL, then the entire vial is 1 mL and a 5,000 IU dose is that whole milliliter. With 2 mL of diluent it is 2 mL. IU is a measure of potency, so the volume it occupies is whatever you dissolved it in.
How many units is 250 IU?
On a 5,000 IU vial reconstituted with 1 mL, each unit carries 50 IU, so 250 IU is 5 units. With 2 mL of diluent each unit carries 25 IU and 250 IU becomes 10 units. With 3 mL it is 15 units.
How many mg is 5,000 IU of hCG?
There is no figure to give. Urinary-derived hCG is labeled in USP units with no mass on the carton at all, while recombinant choriogonadotropin alfa is labeled by mass instead, at 250 mcg per pre-filled syringe. There is no milligram equivalent to read off a 5,000 IU vial. Dose it in IU.
How many IU is 1 mg of somatropin?
3 IU. The 2nd WHO International Standard for somatropin (NIBSC 98/574) assigns 3.0 IU/mg. That factor is what underlies the conversion quoted for growth hormone pens. So 10 mg is 30 IU and 12 mg is 36 IU.
Is an international unit the same as a syringe unit?
No. The shared word causes real dosing errors. A syringe unit is a volume marking: 0.01 mL on a U-100 barrel. An international unit is an amount of biological activity defined separately for each substance. A 500 IU dose is 10 syringe units at one concentration and 50 at another.
Sources & further reading
- NIBSC – 2nd WHO International Standard for Somatropin (98/574), instructions for use: 1.95 mg per ampoule, 3.0 IU/mg for bioassay calibration
- DailyMed – Chorionic Gonadotropin for Injection, USP labeling, showing potency-only labeling (10,000 USP units per multiple-dose vial with diluent)
- FDA-approved labeling for Humulin R (regular insulin human injection): "Markings on the U-100 syringe refer to units of less concentrated insulin products ... and NOT units of HUMULIN R U-500", the clearest official statement that syringe markings belong to one concentration
- OptiPin tools: hCG dose calculator · HGH reconstitution · units to mL · full syringe units chart
The conversions here are arithmetic on the numbers you enter. They cannot confirm the potency actually in your vial, which for compounds sold outside a pharmacy supply chain is the larger uncertainty.
Not medical advice. This is a unit-conversion reference, not a dosing recommendation. It does not tell you what dose to take, whether a compound is appropriate for you, or whether it is legal where you live. Doses should be set with a prescriber. Nothing here should be used to start, change or stop a medication.
OptiPin remembers the reconstitution
Record the vial and the diluent once. Every later dose shows the units to draw and what is left in the vial, on your phone, with no account and nothing in the cloud.
Download on the App Store