Converting ml to mg is dependent on the substance's density. To make this conversion, you'll need to know the substance's density in mg/ml. The formula to use is:
Milliliters (ml) x Density (mg/ml) = Milligrams (mg)
For example, if you have a substance with a density of 1.2 mg/ml and you want to convert 5 ml to mg:
5 ml x 1.2 mg/ml = 6 mg
So, 5 milliliters of a substance with a density of 1.2 mg/ml is equivalent to 6 milligrams.