Insulin syringe unit conversion (revision 24)
Old revision·18:44, 28 Feb 2025·TalkPageTaro
| Insulin syringe unit conversionInteractive reference tool | |
|---|---|
A "unit" is a volume, defined by the syringe, not a quantity of drug. | |
| Inputs | Units, millilitres or mass; concentration; syringe scale |
| Outputs | The other two quantities |
| Scale definitions | |
| U-100 | 100 units = 1 mL; 1 unit = 0.01 mL |
| U-50 | 50 units = 0.5 mL; 1 unit = 0.01 mL on a 0.5 mL barrel |
| U-40 | 40 units = 1 mL; 1 unit = 0.025 mL |
| Standard | ISO 8537 (insulin syringes) |
| Reference tool infobox · conventions | |
An insulin syringe unit is a graduation on a syringe barrel calibrated for insulin of a stated concentration. On the U-100 scale, which is the international standard for human insulin, 100 units correspond to exactly 1 millilitre, so one unit is 0.01 mL.[1] The unit is therefore a volume, and the mass of any substance it contains depends entirely on the concentration of the solution in the barrel.
This is the single most consequential fact on this page, and the source of the errors it exists to prevent. A "10 unit dose" is a statement about volume; it means 0.1 mL, and it says nothing about milligrams until a concentration is supplied. Where a solution has been reconstituted by the user rather than filled by a manufacturer, no syringe marking can carry information about its strength.
Two other scales remain in circulation. U-50 syringes use a 0.5 mL barrel with the same 0.01 mL graduation, giving finer visual resolution for small volumes. U-40 syringes, still used for veterinary insulin in some jurisdictions, place 40 units in 1 mL, so one unit is 0.025 mL — two and a half times the U-100 unit.[1][2]
The converter
[edit]Enter any one of units, volume or mass together with the solution concentration, and the tool reports the other two on the selected scale.
Scale comparison
[edit]| Reading | U-100 volume | U-50 volume | U-40 volume |
|---|---|---|---|
| 5 units | 0.05 mL | 0.05 mL | 0.125 mL |
| 10 units | 0.10 mL | 0.10 mL | 0.25 mL |
| 20 units | 0.20 mL | 0.20 mL | 0.50 mL |
| 40 units | 0.40 mL | 0.40 mL | 1.00 mL |
| 50 units | 0.50 mL | 0.50 mL (full) | — |
| 100 units | 1.00 mL | — | — |
The U-100 and U-50 columns are identical because both use a 0.01 mL graduation; they differ in barrel capacity and therefore in the physical spacing of the marks, which is the point of the U-50 syringe. The U-40 column is the hazardous one: an identical reading corresponds to two and a half times the volume.
A reader who transfers a "20 unit" figure from a U-100 context to a U-40 syringe delivers 0.5 mL instead of 0.2 mL. Reports of this error in the veterinary and human literature are consistent enough that colour-coded caps — orange for U-100, red for U-40 — are conventional.[2]