12mg is a bit high since it's equal or a little stronger than the highest dose of percocet (oxycodone) that you have taken. The other thing is that since the drugs are slightly different you won't have the same tolerance to dilaudid as you do to percocet, so you should start out with a lower dose until you get used to it. 6 or 8mg would be a safer bet, so try 6mg and go from there, adding 2mg if you think you need more, but don't go too high.