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Units and millilitres: a conversion table
The conversion table: what every marking on a U-100 syringe is worth in millilitres.
Last reviewed · written by PepPrep · not medical advice
Insulin syringes are marked in units, and almost everything else in the world is measured in millilitres. This is the lookup table, nothing more — what to measure is between you and a clinician.
On any standard U-100 syringe, 100 units = 1 mL. Every number below follows from that one fact.
| Units | Millilitres | Fits which syringe |
|---|---|---|
| 5 units | 0.05 mL | 0.3 mL · 0.5 mL · 1 mL |
| 10 units | 0.10 mL | 0.3 mL · 0.5 mL · 1 mL |
| 15 units | 0.15 mL | 0.3 mL · 0.5 mL · 1 mL |
| 20 units | 0.20 mL | 0.3 mL · 0.5 mL · 1 mL |
| 25 units | 0.25 mL | 0.3 mL · 0.5 mL · 1 mL |
| 30 units | 0.30 mL | 0.3 mL (full) · 0.5 mL · 1 mL |
| 40 units | 0.40 mL | 0.5 mL · 1 mL |
| 50 units | 0.50 mL | 0.5 mL (full) · 1 mL |
| 75 units | 0.75 mL | 1 mL |
| 100 units | 1.00 mL | 1 mL (full) |
Two things worth remembering. A 0.5 mL syringe holds 50 units, not 50% of something — the barrel size and the unit markings are describing the same capacity two ways. And units are not micrograms: a unit is a measure of volume on the barrel, while mcg and mg measure how much substance is dissolved in that volume. What one unit contains depends entirely on how much liquid was added when the vial was mixed.
If your measurements keep landing between the printed lines, a smaller barrel or a half-unit syringe is the fix. Our measuring guide covers the technique.
"How many units is 2 mg?" — the question with no answer
This is among the most-searched questions about insulin syringes, and it's worth being blunt: as asked, it has no answer. Not because it's a bad question, but because the two things aren't the same kind of measurement.
- Millilitres and units both measure volume — how much liquid. On a U-100 syringe they convert perfectly and permanently: 1 unit is always 0.01 mL, 50 units is always 0.5 mL. The table above never changes.
- Milligrams and micrograms measure mass — how much substance is dissolved in that liquid. Nothing about the syringe tells you this.
So "is 2 mg the same as 20 units?" is like asking whether two kilograms is the same as two litres. It depends entirely on what's dissolved and how concentrated it is — which, for a vial you mixed yourself, is decided by how much water you added.
The same 2 mg can be 20 units, 40 units or 8 units in three vials of identical powder, purely because they were reconstituted with different amounts of liquid. Anyone who gives you a fixed mg-to-units number without asking about your vial and your mixing volume is guessing.
The question that does have an answer is: "my vial contained X mg, I added Y mL, and I want Z mg — how many units is that?" That's three facts and a division, and our calculator does it. If you'd rather do it by hand: divide the vial's mass by the liquid you added to get the concentration per mL, then divide your amount by that, then multiply by 100 to get units.
Supplies mentioned: Syringes & Needles · the calculator