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units to mL calculator
The one syringe conversion that does not depend on what is in the vial.
The short answer
On a U-100 insulin syringe, divide the units by 100. That is the whole conversion. Unlike every other syringe question it does not depend on what is in the vial.
mL = units ÷ 100
So 120 units is 1.2 mL, 80 units is 0.8 mL, 5 units is 0.05 mL. U-100 means 100 units per milliliter, so one unit is 0.01 mL by definition.
The one thing that changes it is a U-40 barrel, still sold for veterinary insulin, where you divide by 40 instead.
Convert your units
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Add the strength printed on your vial to see the dose as well as the volume.
Why this conversion never depends on the drug
Units are the only syringe measurement that is purely geometric. A U-100 barrel is manufactured so that 100 markings span one milliliter, which makes each marking 0.01 mL of whatever liquid you put in it. Testosterone, a reconstituted peptide, hCG, saline: all the same.
Every other conversion on a syringe does depend on the vial. Units to milligrams needs the concentration. Milligrams to units needs it too. Units to volume does not, which is why this is the one number you can safely take from somebody else's post.
Units to mL conversion table
Both syringe standards, with the smallest barrel that holds the draw.
| Units | U-100 | U-40 | Smallest barrel |
|---|---|---|---|
| 1 units | 0.01 mL | 0.025 mL | 0.3 mL |
| 2 units | 0.02 mL | 0.05 mL | 0.3 mL |
| 3 units | 0.03 mL | 0.075 mL | 0.3 mL |
| 4 units | 0.04 mL | 0.1 mL | 0.3 mL |
| 5 units | 0.05 mL | 0.125 mL | 0.3 mL |
| 8 units | 0.08 mL | 0.2 mL | 0.3 mL |
| 10 units | 0.1 mL | 0.25 mL | 0.3 mL |
| 12 units | 0.12 mL | 0.3 mL | 0.3 mL |
| 15 units | 0.15 mL | 0.375 mL | 0.3 mL |
| 20 units | 0.2 mL | 0.5 mL | 0.3 mL |
| 25 units | 0.25 mL | 0.625 mL | 0.3 mL |
| 30 units | 0.3 mL | 0.75 mL | 0.3 mL |
| 40 units | 0.4 mL | 1 mL | 0.5 mL |
| 50 units | 0.5 mL | 1.25 mL | 0.5 mL |
| 60 units | 0.6 mL | 1.5 mL | 1 mL |
| 70 units | 0.7 mL | 1.75 mL | 1 mL |
| 75 units | 0.75 mL | 1.875 mL | 1 mL |
| 80 units | 0.8 mL | 2 mL | 1 mL |
| 90 units | 0.9 mL | 2.25 mL | 1 mL |
| 100 units | 1 mL | 2.5 mL | 1 mL |
| 120 units | 1.2 mL | 3 mL | more than one draw |
| 150 units | 1.5 mL | 3.75 mL | more than one draw |
A U-100 syringe tops out at 100 units, so anything above that is two draws or a larger syringe. For an oil-based injection that volume is usually a sign to split the dose across two sites.
120 units and other draws that will not fit
120 units is 1.2 mL, which is more than a 1 mL insulin syringe holds. If that is the number you arrived at, one of three things is true.
- The dose genuinely needs that volume. Common on higher-dose testosterone at 100 mg/mL. A 3 mL luer-lock syringe is the usual answer rather than two insulin draws.
- The vial is more dilute than it needs to be. For a reconstituted peptide, using less bacteriostatic water puts the same dose into a volume you can actually draw.
- The unit count came from a U-40 barrel. 120 units on U-40 is 3 mL, a very different injection.
Volume also has a practical ceiling per site: a large subcutaneous injection is uncomfortable, which is one of the reasons people give for splitting a weekly dose across two injections. The split dose calculator works out what that leaves per shot.
U-100, U-50 and U-40 are three different rulers
The number after the U is units per milliliter. U-100 is the standard for human insulin and for essentially everything discussed here: 1 unit = 0.01 mL. U-40, sold for veterinary insulin, is 1 unit = 0.025 mL.
Draw a U-100 number on a U-40 barrel and the volume is 2.5× what you intended. The barrels look nearly identical and the printing is small. Check it 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.
Frequently asked questions
How many mL is 120 units?
On a U-100 insulin syringe, 120 units is 1.2 mL. That is more than a 1 mL insulin syringe holds, so it needs either two draws or a larger syringe. On a U-40 barrel the same 120 units would be 3 mL.
How many mL is 80 units?
0.8 mL on a U-100 syringe. It fits a 1 mL barrel with room to spare but not a 0.5 mL one. On U-40 it is 2 mL.
How many mL is 5 units?
0.05 mL on a U-100 syringe. That is a very small volume, so use the smallest barrel you have: in a 0.3 mL syringe it is a sixth of the barrel and easy to read, while in a 1 mL syringe it sits in the first two or three markings.
Does the syringe barrel size change units to mL?
No. A 0.3 mL, 0.5 mL and 1 mL U-100 syringe all place their markings 0.01 mL apart. They differ only in how many markings there are: 30, 50 and 100. Twenty units is 0.2 mL in all three.
How many units is 1 mL?
100 units on a U-100 syringe. That is what U-100 means. On a U-40 syringe 1 mL is 40 units. On U-50 it is 50.
Does the drug in the vial change the volume?
No. Units are a volume marking, so the conversion is the same for testosterone, a reconstituted peptide, hCG or water. What the drug changes is how much dose that volume contains, which is a separate calculation.
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
- OptiPin tools: units to mg · mg to units · full syringe units chart · split dose calculator
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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