China is approximately 9,596,960 sq km, while Brunei is approximately 5,765 sq km, making Brunei 0.06% the size of China. Meanwhile, the population of China is ~1.4 billion people (1.4 billion fewer people live in Brunei).
This to-scale map shows a size comparison of China compared to Brunei. For more details, see an in-depth quality of life comparison of Brunei vs. China using our country comparison tool.