Take the amount you snort to get high and cut it in half just about for how much to do iv. Ime snorting heroin is slightly less than 50% the strength of iv if youre not talking about real high doses.
id start with half a bag to a bag iv, assuming yoive got stamps.
unless youre snorting 4 bags just to get high i reccomend you stick with just sniffing it..i didnt start iving till i would snort half a bundle at a time to get high
but with high amounts snorting ime is like 30% strength of iving. the last time i snorted heroin i snorted a whole bundle at one time, amd at the time id shoot a half bundle to get pretty high. Barely felt anything off the whole bun even though it was the same dope that 5 ivd would get me an acceptable high so if you normally snort large amounts of powder only uae 30% of ypur snorting dose. A bundle is like .5-.8 grams so i didnt get high off of double an iv dose because it took too long to absorb/too much powder.
in short 50% of a snorted dose most of the time but wirh a lot of powder you might only need 33% due to iv being instant and snorting taking time.
a nontolerant user could iv like 50ish mg of "average" street powder heroin ime and be ok/not overdose.
That being said do not iv until you sniff some to test the potency. Ive had the same stamps from the same dealer vary in quality enough that i fell out off of the same amount that was just am average strength shot for 3 weeks of shooting that brand. I thought that i knew how good they were but i was wrong. Exercise caution when you iv heroin but especially wjen you first start. Its easy to do too much and get sick if youre lucky and dont pass out after you do the shot, and its easy to do too little and mess up the rush, because it feels much better to shoot your whole dose at once instead of doing several small shpts within minutes of eachother.
you dont have anybody to show you how much to do? I find it hard to believe that someone whos been using heroin for a year doesnt know anybody who can show them how to IV unless you only get dope off the darknet rather than the street scene/street dealers.