BTU (British Thermal Units-those dang Brits) is the amount of heat needed to bring one pound of water to a boil not the size of the grill. However, the bigger the grill, the more BTUs you will have.Gas grills are typically 20,000 - 50,000 BTU. One tip-you should buy your grill based on how often and how much you grill.eport Abuse. The BTU rating is based on the output of the burners. Basically, the more BTUs, the more heat will come out of your burners. For a regular sized BBQ, I would suggest at least 40 000 BTUs.