Closer than most people guess: Democratic Republic of the Congo (2,334,703 km² km²) is only about 25%% larger than Indonesia (1,872,242 km² km²).
Democratic Republic of the Congo sits in Africa, Indonesia in Asia. On the old Mercator map the latitude gap distorted how large each felt beside the other; at true size the answer is simply 1.2×.
The old Mercator map treated both about equally (1× vs 1× inflation), so at least their relative sizes were preserved — even if both were drawn at the wrong absolute scale.
Indonesia fits 1× into Democratic Republic of the Congo.