This a very poor thing to judge things by bases in this number or frame is thinking alone.
I am not trying to say one side or the other would win but only bring about a topic if relevance to the stupidity of your observation.
The US is about 350 million people… China is about 1.2 billion
This about the same percentage… who would win?
This is not a good idea in my mind in any of these things of war this why I like to place in this term. I am not suggesting that any countries go to war let along nuclear capable ones.
However to show you a relevant example this is what I would bring your attention to.