Mozambique is about 2.3 times bigger than Republic of the Congo.

Republic of the Congo is approximately 342,000 sq km, while Mozambique is approximately 799,380 sq km, making Mozambique 134% larger than Republic of the Congo. Meanwhile, the population of Republic of the Congo is ~5.5 million people (26.1 million more people live in Mozambique).
Tip: This to-scale comparison of Republic of the Congo vs. Mozambique uses the Mercator projection, which distorts the size of regions near the poles.