Start with three numbers
The vial label tells you the total amount. The liquid tells you how concentrated it is. The amount you enter tells the calculator which portion to measure. These are three different things.
A simple calculation
Example only: 10 mg in 2 mL equals 5 mg/mL. An entered amount of 300 mcg is 0.3 mg, which occupies 0.06 mL. With 20 mg in the same 2 mL, that amount occupies 0.03 mL. A larger vial does not call for a larger amount.
Keep the units visible
A U-100 scale has 100 unit markings per mL. Those markings describe volume; they are not mg, mcg or a drug’s biological IU. FDA has reported serious errors from confusing these measures with compounded semaglutide. Confirm the actual product concentration and measuring device with your clinician or pharmacist.