How is the concentration of IV contrast measured?

In milligrams of iodine (I) per milliliter of injectable.
This makes the total dose to the patient calculable: 100 mL of 300 mg I/mL=30 g I, and 100 mL of 350 mg I/mL = 35 g I.
If possible, the dose in any 24 hour period is usually limited to 60 g of Iodine