August 2, 2026
Units vs mL vs mg: The Complete Insulin Syringe Conversion Guide
Convert between syringe units, millilitres and milligrams on U-100, U-50 and U-40 insulin syringes. Printed conversion tables for every common dose, plus the one formula that ties them together.
Three different numbers describe the same injection, and mixing them up is the single most common source of dosing errors: units (marks on the syringe barrel), millilitres (actual liquid volume), and milligrams or micrograms (how much drug). They are not interchangeable, and no chart can convert milligrams to units without one extra piece of information.
This guide covers every direction of that conversion, with a printed table for each. Bookmark it — the tables are the point.
The one rule that makes all of this simple
A syringe measures volume, not drug. The "units" printed on an insulin syringe are just a volume scale with a different name.
On a standard U-100 insulin syringe, 100 units = 1 mL. So:
- 1 unit = 0.01 mL
- To go from units to mL: divide by 100
- To go from mL to units: multiply by 100
That is the entire relationship. Everything else on this page is that rule applied to different starting numbers, or the extra step needed when milligrams are involved.
Units to mL on a U-100 syringe
| Units | Millilitres | Also written as |
|---|---|---|
| 2 units | 0.02 mL | — |
| 4 units | 0.04 mL | — |
| 5 units | 0.05 mL | — |
| 10 units | 0.10 mL | 1/10 mL |
| 15 units | 0.15 mL | — |
| 20 units | 0.20 mL | 1/5 mL |
| 25 units | 0.25 mL | 1/4 mL |
| 30 units | 0.30 mL | — |
| 35 units | 0.35 mL | — |
| 40 units | 0.40 mL | — |
| 50 units | 0.50 mL | half a millilitre |
| 60 units | 0.60 mL | — |
| 75 units | 0.75 mL | 3/4 mL |
| 80 units | 0.80 mL | — |
| 100 units | 1.00 mL | a full millilitre |
So when someone asks what 40 units means in volume, the answer is 0.4 mL on a U-100 syringe — a little under half a millilitre.
mL to units on a U-100 syringe
| Millilitres | Units |
|---|---|
| 0.02 mL | 2 units |
| 0.05 mL | 5 units |
| 0.10 mL | 10 units |
| 0.15 mL | 15 units |
| 0.20 mL | 20 units |
| 0.25 mL | 25 units |
| 0.30 mL | 30 units |
| 0.40 mL | 40 units |
| 0.50 mL | 50 units |
| 0.60 mL | 60 units |
| 0.75 mL | 75 units |
| 1.00 mL | 100 units |
1 mL equals 100 units on a U-100 syringe. That single fact answers most of the questions people arrive with.
The syringe factor: U-100 vs U-50 vs U-40
Not every insulin syringe uses the same scale. The number after the U is how many units fit in one millilitre.
| Syringe | Units per mL | 1 unit equals |
|---|---|---|
| U-100 (standard) | 100 | 0.010 mL |
| U-50 | 50 | 0.020 mL |
| U-40 (common in veterinary use) | 40 | 0.025 mL |
The general formula covering all three:
mL = units ÷ syringe factor
To convert a unit count between scales so that the same volume is delivered:
- U-100 to U-40: multiply the units by 0.4
- U-40 to U-100: multiply the units by 2.5
- U-100 to U-50: multiply the units by 0.5
| Volume | U-100 reads | U-50 reads | U-40 reads |
|---|---|---|---|
| 0.10 mL | 10 units | 5 units | 4 units |
| 0.20 mL | 20 units | 10 units | 8 units |
| 0.25 mL | 25 units | 12.5 units | 10 units |
| 0.50 mL | 50 units | 25 units | 20 units |
| 1.00 mL | 100 units | 50 units | 40 units |
Reading a U-40 syringe as though it were U-100 delivers 2.5 times the intended volume. This is a genuine safety issue, not a technicality — always check the barrel before you draw.
Why milligrams need one more number
Here is where most charts online quietly mislead people. You cannot convert milligrams to units with a fixed table, because a milligram is an amount of drug and a unit is an amount of liquid. The bridge between them is your vial's concentration.
Concentration (mg/mL) = mg in the vial ÷ mL of BAC water you added
Then:
Units on a U-100 = (your dose in mg ÷ concentration in mg/mL) × 100
Two people can both draw 20 units and receive completely different amounts of drug, because they reconstituted their vials differently. This is why "how many units is 2 mg" has no single answer.
How many units is 2 mg?
It depends entirely on how you mixed the vial. Every row below delivers exactly 2 mg.
| Concentration | Volume for 2 mg | Units on U-100 |
|---|---|---|
| 10 mg/mL | 0.20 mL | 20 units |
| 5 mg/mL | 0.40 mL | 40 units |
| 3.33 mg/mL | 0.60 mL | 60 units |
| 2.5 mg/mL | 0.80 mL | 80 units |
| 2 mg/mL | 1.00 mL | 100 units |
The person drawing 80 units is not taking four times as much drug as the person drawing 20 units. They are taking the same 2 mg spread through more water.
How many units is 100 mcg? And 500 mcg?
Micrograms work identically — there are 1000 mcg in 1 mg, so convert first.
| Dose | Concentration | Volume | Units on U-100 |
|---|---|---|---|
| 100 mcg | 1 mg/mL | 0.10 mL | 10 units |
| 100 mcg | 2 mg/mL | 0.05 mL | 5 units |
| 100 mcg | 5 mg/mL | 0.02 mL | 2 units |
| 250 mcg | 2.5 mg/mL | 0.10 mL | 10 units |
| 500 mcg | 1 mg/mL | 0.50 mL | 50 units |
| 500 mcg | 2.5 mg/mL | 0.20 mL | 20 units |
| 500 mcg | 5 mg/mL | 0.10 mL | 10 units |
Notice the pattern: at 5 mg/mL a 100 mcg dose is only 2 units. That is a very small mark to read accurately, which is the practical argument for reconstituting with more water when your doses are small.
What "100 units to mg" actually means
This question comes up constantly and it has no fixed answer either. 100 units is 1 mL. How many milligrams sit in that millilitre is your concentration.
| Concentration | 100 units (1 mL) contains |
|---|---|
| 1 mg/mL | 1 mg |
| 2 mg/mL | 2 mg |
| 5 mg/mL | 5 mg |
| 10 mg/mL | 10 mg |
| 15 mg/mL | 15 mg |
If someone tells you "100 units equals X mg" without asking about your vial, they are guessing.
Worked example, start to finish
You have a 10 mg vial. You add 2 mL of bacteriostatic water. Your prescriber has told you to take 0.5 mg.
- Concentration: 10 mg ÷ 2 mL = 5 mg/mL
- Volume needed: 0.5 mg ÷ 5 mg/mL = 0.1 mL
- Units on a U-100: 0.1 mL × 100 = 10 units
Draw to the 10 mark. If you had used 3 mL of water instead, the same 0.5 mg would sit at 15 units — same drug, different mark.
Four mistakes that cause real dosing errors
- Reading a U-40 syringe as U-100. Delivers 2.5× the intended volume. Check the barrel every time.
- Treating mg and units as fixed partners. They are only related through your specific vial's concentration.
- Assuming 1 mL is 1 unit. It is 100 units on a standard syringe. This one shows up in emergency rooms.
- Confusing cc and mL with units. 1 cc is exactly 1 mL, which is 100 units — cc and mL are the same thing, units are not.
Quick reference
- 1 mL = 100 units (U-100) = 50 units (U-50) = 40 units (U-40)
- 1 unit on U-100 = 0.01 mL
- mL = units ÷ syringe factor
- units = mL × syringe factor
- concentration (mg/mL) = vial mg ÷ BAC water mL
- units for a dose = (dose mg ÷ concentration) × syringe factor
FAQ
Is 1 mL the same as 1 unit? No. On a standard U-100 insulin syringe 1 mL is 100 units. Treating them as equal is a 100-fold error.
How many units is 1 mL? 100 units on a U-100 syringe, 50 on a U-50, and 40 on a U-40.
Is 1 cc the same as 1 mL? Yes, exactly. A cubic centimetre and a millilitre are the same volume. Neither is the same as a unit.
What is 0.25 mL in units? 25 units on a U-100 syringe, 10 units on a U-40.
Why does my dose look like a different number of units than someone else's? Because you reconstituted with different amounts of bacteriostatic water. Different concentration, different volume, same milligrams.
Do I multiply or divide to get from units to mL? Divide by the syringe factor. Units to mL divides; mL to units multiplies.
This article is for informational purposes only and is not medical advice. Confirm every dose and syringe reading with a licensed prescriber or pharmacist before injecting.