You are supposed to be using 500mcg or HCG per shot, not iu.
iu is just a measure of volume, the way ml or cc is.
So, if you have a 1,500mcg vial of hcg powder, if you add 1.5ml of water to it, then you will have 500mcg for every 1/2ml of water.
Or if you add 3ml of water, you will have 500mcg/ml