How do you convert vitamin D IU to mg?

1 mcg vitamin D (cholecalciferol) = 40 IU

Let´s say you have 300 IU of vitamin D: 300 / 40 = 7,5 mcg vit. D

Then you would have to convert 7,5 mcg to mg: 7,5 / 1000 = 0,0075 mg vitamin D.