How long is a piece of string?
It varies widely. There is no conversion. There's not even any regional consistency and often no local consistency or even consistency from package to package. There is crap tar cut with God only knows what tarry substance, fire tar that will stand up to most any ECP, and there is ECP that has taken so many whacks you can barely even call it dope anymore. There is good dope in Kentucky and shit dope in New York City. There is fire soft in Alaska and shit soft in Florida. All who you know and who they know.
The only way to know is to know your source and your product (preferably quantitatively but this is out of reach for most, so the rule "start low and go slow" must always apply.)