How much weed in a joint?
You can roll however much you want when rolling a joint, and papers come in a variety of sizes, so there’s no one right answer.
The pre-rolled j’s you buy from a dispensary are filled with ~1 gram of shake, though you can find some pretty big ones out there. I’ve seen up to a quarter ounce joints in dispensaries.
Just remember those pre-rolled joints are filled with the garbage they couldn’t sell on its own.