Insulin syringe unit converter
Units to millilitres and back on a U-100 syringe, and the dose-to-units conversion for whatever concentration is in your vial. Free, no account.
U-100 means one hundred units per millilitre. That single sentence settles most of the confusion around insulin syringes: the "100" is a concentration marking, not a capacity. A 0.3 ml syringe, a 0.5 ml syringe and a 1 ml syringe are all U-100, so 0.1 ml is ten units on every one of them. What the barrel size decides is only how far the scale goes — 30, 50 or 100 units.
Worked through: a vial at 2,500 mcg/ml and a dose of 250 mcg. Volume is 250 ÷ 2,500 = 0.1 ml, and 0.1 ml × 100 = 10 units. Halve the concentration to 1,250 mcg/ml and the same dose becomes 0.2 ml, or 20 units — the same drug, twice the liquid, twice the number on the barrel.
How the math works
units = volume (ml) × 100 (U-100: 100 units per ml)
ml = units ÷ 100
Two rules the calculator applies. A draw is rounded to the nearest half-unit, because that is the finest mark an insulin syringe carries and reading between marks against a meniscus is not measurement. And a draw under two units is flagged rather than reported cleanly: at that size the error in reading the barrel is a large fraction of the dose, and the fix is a more dilute solution rather than a steadier hand.
The conversions people look up
These hold for any U-100 syringe regardless of barrel size. Where a row says "over the barrel", the volume is larger than that syringe holds.
| Volume | Units (U-100) | 0.3 ml barrel | 0.5 ml barrel | 1 ml barrel |
|---|---|---|---|---|
| 0.05 ml | 5 units | 5 u | 5 u | 5 u |
| 0.1 ml | 10 units | 10 u | 10 u | 10 u |
| 0.15 ml | 15 units | 15 u | 15 u | 15 u |
| 0.2 ml | 20 units | 20 u | 20 u | 20 u |
| 0.25 ml | 25 units | 25 u | 25 u | 25 u |
| 0.3 ml | 30 units | 30 u | 30 u | 30 u |
| 0.4 ml | 40 units | over the barrel | 40 u | 40 u |
| 0.5 ml | 50 units | over the barrel | 50 u | 50 u |
| 0.75 ml | 75 units | over the barrel | over the barrel | 75 u |
| 1 ml | 100 units | over the barrel | over the barrel | 100 u |
Questions people actually ask
Is a unit the same as a millilitre?
No, and conflating the two is the most expensive mistake in this whole area. On a U-100 syringe a unit is one hundredth of a millilitre. "10 units" and "10 ml" differ by a factor of a hundred.
Is a unit a fixed amount of drug?
Not for anything measured this way. For insulin itself a unit is a defined international unit of activity, and U-100 insulin is formulated so that one unit occupies 0.01 ml — which is where the marking comes from. For a reconstituted peptide there is no such standard: a unit is purely a volume, so how much drug it contains depends entirely on the concentration you mixed. This is why "how many units should I take" has no answer without a concentration.
What about U-40 or U-50 insulin syringes?
U-40 syringes exist (mostly veterinary) and are marked 40 units to the millilitre, so a unit there is 0.025 ml. Mixing a U-40 syringe with a U-100 assumption over-doses by two and a half times. The syringes people describe as "U-50" are almost always 0.5 ml U-100 barrels marked to 50 — still a hundred units per millilitre. Check the barrel, not the box.
Why does my draw not land on a mark?
Because the concentration was not chosen with the dose in mind. Adjusting the diluent volume moves every future draw onto a round number — that is what the reconstitution calculator's reverse solver is for.
The app stores each vial’s concentration and shows the draw in units next to a syringe diagram, so the conversion happens once rather than every injection.
Save this dose to your logThis calculator does the arithmetic you typed and nothing else. It does not know what is actually in your vial, whether the label is accurate, or anything about you. Confirm the vial strength and the diluent volume on your own label before you draw, and take dosing decisions to a qualified provider.