iu measures the dosage of the HCG, it is not a per se measurement of volume. For example, 1cc doesn't equal any set amount of iu's
That being said, for example, your HCG vial will state it has 1000iu (if it is 1000iu of course). You take roughly 1cc of BAC and inject it into the HCG. Suck it out and then you have roughly 1cc of 1000iu HCG. If you want 250iu's then take 1/4 of it.