The exact tracking range of a Bluetooth tracker will vary from product to product, but you can generally expect a tracking range of 30 to 300 feet. This range, however, can go down considerably if there are a lot of obstacles between your phone and the tracker.
Some item finders, like Apple's AirTag, remove the limit on their tracking range — this specific Bluetooth tracker uses all the Apple devices in the world to transmit the location of whatever it is you’re tracking. This means that as long as your AirTag is near an iPhone or similar Apple product, you'll be able to track it with your phone.