Units are not a volume
A millilitre is a millilitre everywhere. A unit is a mark on one particular barrel, and the volume behind it depends entirely on how that barrel was calibrated.
Educational arithmetic only. Not medical advice and not a dosing protocol.
The same number, three volumes
Insulin syringes are calibrated so that a stated number of units fills one millilitre. A U-100 carries a hundred, a U-50 carries fifty, a U-40 carries forty. The printed scale is a volume scale with a conversion factor built into it, and the factor is not the same on every barrel.
So a reading of twenty means 0.2 mL, 0.4 mL or 0.5 mL depending on which syringe is in the drawer. The syringe will not object either way, and nothing about the number on the page would look different.
| Reading | U-100, 1 mL | U-100, 0.5 mL | U-100, 0.3 mL | U-50, 0.5 mL | U-40, 1 mL |
|---|---|---|---|---|---|
| 5 units | 0.050 mL | 0.050 mL | 0.050 mL | 0.100 mL | 0.125 mL |
| 10 units | 0.100 mL | 0.100 mL | 0.100 mL | 0.200 mL | 0.250 mL |
| 20 units | 0.200 mL | 0.200 mL | 0.200 mL | 0.400 mL | 0.500 mL |
| 30 units | 0.300 mL | 0.300 mL | 0.300 mL | past the barrel | 0.750 mL |
| 50 units | 0.500 mL | 0.500 mL | past the barrel | past the barrel | past the barrel |
Before you act on that number
This is educational arithmetic on figures entered by the reader. It is not medical advice, not a dosing protocol, and not a recommendation that anything be prepared, obtained or administered.
Nothing here states what quantity is appropriate for anyone, and there is no function in it that produces an amount to administer. A question about anyone’s health belongs with a licensed clinician who can examine the person asking.
Compounds of the kind this arithmetic is used on are largely research chemicals that are not approved by the FDA for human use. An exact calculation is not an accurate measurement: what is actually in a syringe depends on the preparation and the device, neither of which this page can see.
No qualified clinical reviewer is recorded against this site, and no credential is claimed anywhere on it. what this is not, at full length.
Why a default would be worse than a question
U-100 is the most common calibration in most markets, and that is exactly what makes defaulting to it hazardous. The assumption is right often enough to go unchallenged and wrong by a factor of two or two and a half when it fails. An error that is usually invisible and occasionally large is worse than one that is always visible.
So the barrel field on every panel here starts empty, and the panels refuse to produce a reading without it. It is the only field on this site with that kind of friction, and it is deliberate.
Capacity is a different number and gets confused with calibration
A U-100 barrel can hold 1 mL, 0.5 mL or 0.3 mL. All three are U-100, all three read the same number for the same volume, and only one of them can take eighty units. Calibration tells you what a mark means; capacity tells you how many marks there are.
Which is why a reading can be arithmetically correct and physically impossible. The panels here say so rather than printing a number the device cannot deliver, and volume into units carries the full comparison.
Related
- Short draws and reading error
What the calibration costs in accuracy as well as in meaning.
- Volume into units
The conversion on its own, in either direction.
- The calculator
Where the barrel field sits in the main conversion.