Australia dwarfs Mongolia: about 7,706,009 km² km² against 1,560,428 km² km². At true size Australia is about 4.9× larger — the whole of Mongolia fits into Australia roughly 4 times.
Australia sits in Oceania, Mongolia 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 4.9×.
The old map muddied it further: Mercator inflates Australia about 1.2× and Mongolia about 2.2×, so on a Mercator-style map this pair appears 2.8× apart instead of the true 4.9×.
Mongolia fits 4× into Australia.