I want to buy a Raspberry Pi 3 Model B, but I want to know what the range of the Bluetooth is.
It has in-built Bluetooth 4.1.
The range depends on various factors like
You can have a good connectivity within a 60-70 mts range for Bluetooth 4.1. I have used at my home but at times it disconnects. I am using a Raspberry Pi 2 with a Bluetooth adapter connected to the AmazonBasics Bluetooth speakers.
check the Bluetooth documentation (bluez) for more details.