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units to mg calculator
How much drug is in the units you drew? The syringe cannot tell you – the concentration can.
The short answer
Units measure volume, not drug. On a U-100 syringe one unit is 0.01 mL, so how much drug it carries is decided entirely by the strength of the liquid you drew it from.
mg = units × (concentration in mg/mL ÷ 100)
So 10 units is 1 mg at 10 mg/mL, 20 mg at 200 mg/mL, 0.1 mg at 1 mg/mL. Same 10 units, a two hundred-fold spread in dose.
A unit count posted without its concentration cannot be converted. If you are reading somebody else's number, that is the first thing to ask for.
Convert your units
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A "100 unit syringe" is a size, not a strength
Questions like "what is 300 mcg on a 100 unit syringe" contain one number that does not help. The 100 is the barrel capacity: a 1 mL syringe holds 100 units. It tells you nothing about what is inside, so it cannot change the conversion.
A dose is the same number of units in a 0.3 mL, 0.5 mL or 1 mL U-100 syringe. The only thing that changes with barrel size is how finely the markings are printed. Smaller barrels spread the same units over more distance, which is why a small dose is more accurately measured in a 0.3 mL syringe.
What does change the conversion is U-100 versus U-40, which is a different definition of the unit itself rather than a different size.
Units to micrograms, by reconstitution
For peptides the useful intermediate is micrograms per unit: vial mg × 10, divided by the mL of bacteriostatic water you added. Find your column, then read down to the units you drew.
| Units drawn | 10 mcg/unit 5 mg + 5 mL | 20 mcg/unit 10 mg + 5 mL | 25 mcg/unit 5 mg + 2 mL | 50 mcg/unit 10 mg + 2 mL | 100 mcg/unit 10 mg + 1 mL |
|---|---|---|---|---|---|
| 1 units | 10 | 20 | 25 | 50 | 100 |
| 2 units | 20 | 40 | 50 | 100 | 200 |
| 4 units | 40 | 80 | 100 | 200 | 400 |
| 5 units | 50 | 100 | 125 | 250 | 500 |
| 8 units | 80 | 160 | 200 | 400 | 800 |
| 10 units | 100 | 200 | 250 | 500 | 1000 |
| 15 units | 150 | 300 | 375 | 750 | 1500 |
| 20 units | 200 | 400 | 500 | 1000 | 2000 |
| 25 units | 250 | 500 | 625 | 1250 | 2500 |
| 30 units | 300 | 600 | 750 | 1500 | 3000 |
| 40 units | 400 | 800 | 1000 | 2000 | 4000 |
| 50 units | 500 | 1000 | 1250 | 2500 | 5000 |
All figures in micrograms, on a U-100 syringe. Divide by 1000 to read them as milligrams.
Units to milligrams on testosterone and other oils
Oil vials arrive pre-mixed, so the strength is printed on the label and there is no reconstitution step. Milligrams per unit is simply the concentration divided by 100.
| Units drawn | 100 mg/mL | 200 mg/mL | 250 mg/mL |
|---|---|---|---|
| 10 units | 10 mg 0.1 mL | 20 mg 0.1 mL | 25 mg 0.1 mL |
| 20 units | 20 mg 0.2 mL | 40 mg 0.2 mL | 50 mg 0.2 mL |
| 25 units | 25 mg 0.25 mL | 50 mg 0.25 mL | 62.5 mg 0.25 mL |
| 40 units | 40 mg 0.4 mL | 80 mg 0.4 mL | 100 mg 0.4 mL |
| 50 units | 50 mg 0.5 mL | 100 mg 0.5 mL | 125 mg 0.5 mL |
| 60 units | 60 mg 0.6 mL | 120 mg 0.6 mL | 150 mg 0.6 mL |
| 75 units | 75 mg 0.75 mL | 150 mg 0.75 mL | 187.5 mg 0.75 mL |
| 80 units | 80 mg 0.8 mL | 160 mg 0.8 mL | 200 mg 0.8 mL |
| 100 units | 100 mg 1 mL | 200 mg 1 mL | 250 mg 1 mL |
The volume in grey is the same whatever the concentration, because units are a volume measurement.
Check the barrel says U-100
Every figure on this page assumes a U-100 syringe: 100 units per mL, so one unit is 0.01 mL. U-40 syringes are still sold for veterinary insulin at 40 units per mL, where one unit is 0.025 mL.
Reading a U-40 draw with the U-100 table under-states the dose by 2.5 times. The two barrels look nearly identical, so check before every new box.
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.
Doing it without the calculator
- 1. Volume. Units ÷ 100 = mL on a U-100 syringe. This step never changes.
- 2. Strength. Vial mg ÷ mL of water = mg per mL. Skip it if the strength is printed on the vial.
- 3. Dose. mL × mg per mL = your dose in mg. Multiply by 1000 for micrograms.
Worked example: 8 units on a U-100 syringe is 0.08 mL. A 5 mg vial with 2 mL of water is 2.5 mg/mL. So 0.08 × 2.5 = 0.2 mg, which is 200 mcg.
Frequently asked questions
How much is 300 mcg in a 100 unit syringe?
The barrel size does not affect it. What matters is the concentration. At 50 mcg per unit, 300 mcg is 6 units. At 25 mcg per unit it is 12 units, at 100 mcg per unit it is 3 units. A 10 mg vial reconstituted with 2 mL of bacteriostatic water gives 50 mcg per unit.
How many mcg is 10 units?
Multiply 10 by your micrograms per unit. A 5 mg vial with 2 mL of water is 25 mcg per unit, so 10 units is 250 mcg. A 10 mg vial with 1 mL of water is 100 mcg per unit, so the same 10 units is 1000 mcg. The unit count is identical, the dose is four times larger.
What is 2 mg on a 100 unit syringe?
Work backwards from the concentration. At 10 mg/mL, 2 mg is 0.2 mL, which is 20 units. At 20 mg/mL it is 10 units, at 5 mg/mL it is 40 units. On a 1 mL barrel all three fit comfortably.
Is there a fixed conversion from insulin units to mg?
Only for insulin itself, the drug the syringe was designed for, where one unit is a defined amount of biological activity. For anything else drawn from a vial the unit is purely a volume marking, so the conversion is different for every concentration.
How do I find my micrograms per unit?
Multiply the vial strength in milligrams by 10, then divide by the milliliters of bacteriostatic water you added. A 10 mg vial with 2 mL of water is (10 x 10) divided by 2 = 50 mcg per unit. Write that number on the vial as soon as you mix it.
Why do two people on the same dose draw different units?
Because they reconstituted differently. One person using 1 mL of bacteriostatic water and another using 3 mL will correctly draw unit counts three times apart for an identical dose. Neither is wrong, which is why unit counts are not transferable between people.
Sources & further reading
- 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
- ISMP, Nurse Advise-ERR, August 2017 – "Problems associated with the use of U-500 insulin syringes": measuring one concentration on another concentration's barrel gives a five-fold error
- DailyMed – Bacteriostatic Water for Injection labeling
- OptiPin tools: mg to units · units to mL · full syringe units chart · reconstitution calculator
The arithmetic here is exact and follows from the definition of U-100. What it cannot verify is what is actually in your vial. Underfilled or mislabeled vials are common enough in this space that the calculation is the floor of your diligence rather than the ceiling.
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.
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