Units and millilitres
U-100 means the syringe is marked for 100 units in every millilitre. One unit is 0.01 mL, and the size of a unit is the same on every U-100 syringe, large or small.
To turn units into mL, divide by 100: 25 units is 0.25 mL. To turn mL into units, multiply by 100.
What the lines mean
- 1 mL (100 units): numbers every 10 units, each small line usually 2 units.
- 0.5 mL (50 units): numbers every 5 units, each small line usually 1 unit.
- 0.3 mL (30 units): numbers every 5 units, each small line usually 1 unit. Some 0.3 mL syringes also have half-unit lines.
- Brands differ. Always count the lines between two numbers on your own syringe before you rely on them.
Where to read the plunger
Line up the flat edge of the black rubber seal that is closest to the needle with the mark. Do not read from the far end of the seal or from the domed tip.
Air bubbles take up space in the barrel, so a reading with a bubble in it holds less liquid than the mark shows. Your pharmacist or nurse can show you how to remove them.
U-100 and U-40 are different scales
A U-40 syringe is marked for 40 units per mL, so its units are larger. Numbers from a U-100 calculation do not carry over to a U-40 syringe. Check the U- marking on the package and on the barrel.
