On the vitamin bottle some say iu and others say mg what is the difference between like
1mg and 1iu in measurements

IU stands for International Units and is used for the measurement of drugs and vitamins.

Webster's defines IU as: a quantity of a biologic (such as a vitamin) that produces a particular biological effect agreed upon as an international standard

What this means is that IU is dependent on the potency of the substance, and each substance would have a different IU to milligram conversion. For example, 1000 IU of Vitamin C would have a different weight than 1000 IU of Vitamin A

Since each substance would have a different conversion ratio, we cannot put up a conversion for IU to milligrams that covers everything, or even most things. Just too many different substances.

Just know the recommendations on the bottle you buy. It's hard to OD on vitimans unless you are taking mass doses. Don't over do it with Iron or A. If it says take one a day,, take one a day.