Closer than most people guess: Australia (7,706,009 km² km²) is only about 22%% larger than China (9,371,225 km² km²).
Australia sits in Oceania, China 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 map muddied it further: Mercator inflates Australia about 1.2× and China about 1.6×, so on a Mercator-style map this pair appears 1.5× apart instead of the true 1.2×.
Australia fits 1× into China.