Glossary
Insulin Syringe Units (U-100)
On a U-100 syringe, 100 units equal 1 mL, so each unit is 0.01 mL. Units mark volume, not peptide content — here is how to convert them correctly in the lab.
The scale on a U-100 insulin syringe is based on insulin concentration: 100 international units of U-100 insulin fill 1 mL, so the graduations go from 0 to 100 over one millilitre and every unit corresponds to 0.01 mL. A 0.5 mL barrel uses the same 0.01 mL per unit, with graduations up to 50.
Units are volume marks
The essential point: a unit marks a volume and says nothing about how much peptide is present. It only had a meaning in terms of substance for insulin, because insulin was standardised at 100 units per millilitre. With any reconstituted research peptide, the amount contained in ten units depends solely on the concentration created during reconstitution. For example, a 5 mg vial dissolved in 2 mL yields 2.5 mg/mL; 10 units (0.10 mL) then hold 250 mcg and 1 unit holds 25 mcg. Reconstituting the same vial in 1 mL instead gives 50 mcg per unit.
For this reason, record the vial concentration on the label rather than a number of units. Choosing a syringe also means considering gauge and barrel volume — see 31G 1 mL syringes, 29G 0.5 mL syringes and the syringe selection guide.
Related terms
micrograms vs milligrams · luer-lock · syringes and vials