Australia dwarfs Saudi Arabia: about 7,706,009 km² km² against 1,925,871 km² km². At true size Australia is about 4× larger — the whole of Saudi Arabia fits into Australia roughly 4 times.
Australia sits in Oceania, Saudi Arabia 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×.
The old Mercator map treated both about equally (1.2× vs 1.2× inflation), so at least their relative sizes were preserved — even if both were drawn at the wrong absolute scale.
Saudi Arabia fits 4× into Australia.