China dwarfs Mexico: about 9,371,225 km² km² against 1,962,279 km² km². At true size China is about 4.8× larger — the whole of Mexico fits into China roughly 4 times.
China 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 4.8×.
The old map muddied it further: Mercator inflates China about 1.6× and Mexico about 1.2×, so on a Mercator-style map this pair appears 6.2× apart instead of the true 4.8×.
Mexico fits 4× into China.