Nearly a tie: China and United States differ by barely 1%% in area — about 9,371,225 km² km² against 9,439,424 km² km².
China sits in Asia, United States 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 map muddied it further: Mercator inflates China about 1.6× and United States about 2×, so on a Mercator-style map this pair appears 1.3× apart instead of the true 1×.
China fits 1× into United States.