Concentration, without confusion.
Mass, liquid volume, concentration, and syringe markings describe different quantities.
A milligram is a unit of mass. A milliliter is a unit of volume. Concentration expresses how much material is present in a volume; the two inputs must remain explicit.
The prefix milli means one thousandth and micro means one millionth. Therefore 1 mg equals 1,000 mcg. A calculator must convert units before dividing a target mass by concentration.
Syringe markings are a volume scale when interpreted against a particular calibration. A U-100 scale has 100 marked units per mL; it does not tell you the biological activity units of another medicine.
Peptoryn’s calculators show arithmetic from your inputs. They do not select a dose or establish chemical compatibility, stability, sterility, or suitability for injection.