Heroin is nothing like prescription opioids. There is know way of knowing what you strength you are buying! It's not like someone says "Hey got some 10's" and you know ok i'm getting exactly 10mg of a dose. The only way of knowing how pure or strong the stuff you got is to snort a small amount about the size of a match head and wait 30 minutes and see how you feel. If that doesn't get you to the point you want then try another match head sized bump. always start super small and slowly work your way up(always). It's not worth dying over being to impatient to wait to see how strong it is.
But I strongly advise you not to go to heroin it only gets worse because its cheaper and sometimes even stronger which sounds great until you find out what that addiction really is... A monster! I can't really talk because I snort H almost everyday. Heads up though it only gets worse after the high becomes harder and harder to achieve.