U-100 syringe

A U-100 syringe is an insulin-style syringe with a barrel marked in “units” instead of milliliters. The “100” means the scale is calibrated so that 100 units equal 1 mL — which puts each single unit at exactly 0.01 mL.

What the units actually measure

The unit marks on a U-100 syringe measure volume, not any specific drug amount. A unit is always 0.01 mL of whatever liquid is in the barrel — water, saline, or a reconstituted peptide solution. How much active substance sits in that 0.01 mL depends entirely on the concentration of the liquid, which is set during reconstitution by how much diluent was added to the vial. The same unit mark can represent very different amounts of substance depending on that concentration.

U-100 vs. other scales

Not every syringe uses the U-100 scale — U-40 syringes exist too, with 40 units per mL instead of 100, so unit marks aren’t interchangeable across syringe types. Reading a dose off the wrong scale changes the volume being measured, since the math (units ÷ scale = mL) is different for each.

Turning a concentration into a syringe reading

Once a solution’s concentration is known — from the vial amount in mg or mcg and the liquid added — that concentration can be converted into where a given volume falls on a U-100 syringe’s unit scale. The mg-to-units calculator does exactly that conversion on the vial size, dilution, and target amount you enter; it never suggests what to draw, only the arithmetic behind the number on the barrel.