Nearly a tie: Indonesia and Mexico differ by barely 5%% in area — about 1,872,242 km² km² against 1,962,279 km² km².
Indonesia sits in Asia, Mexico in North America. On the old Mercator map the latitude gap distorted how large each felt beside the other; at true size the answer is simply 1×.
The old Mercator map treated both about equally (1× vs 1.2× inflation), so at least their relative sizes were preserved — even if both were drawn at the wrong absolute scale.
Indonesia fits 1× into Mexico.