btu calculation formula for air conditioner

Advise something, please. I want to buy an air conditioner.

My friend wanted to buy an air conditioner for himself, but he did not know which one he wanted to take and what characteristics would be suitable for his apartment. He had a rather spacious apartment and was afraid that after the purchase the air conditioner would not be powerful enough, but at the same time, the air conditioner could strongly affect the power grid and it could burn out. Whatever all this happens, I advised him to calculate the required power of his future air conditioner using this blog btu calculation formula for air conditioner . Everything is written there simply and clearly, it is very easy to calculate, only you need to know the dimensions as accurately as possible so as not to be mistaken.