Nearly a tie: Mexico and Indonesia differ by barely 3% in area: about 1,964,375 km² against 1,904,569 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 1.03×.
The old Mercator map treated both about equally (1.00× 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.
Indonesia vs Mexico: key figures
| Measure | Indonesia | Mexico |
|---|
| True area | 1,904,569 km² · #15 | 1,964,375 km² · #14 |
| Mercator inflation | 1.00× | 1.2× |
| Apparent on Mercator | 1,907,616 km² | 2,350,964 km² |