Europe dwarfs Mongolia: about 10,180,000 km² km² against 1,560,428 km² km². At true size Europe is about 6.5× larger — the whole of Mongolia fits into Europe roughly 6 times.
The old Mercator map treated both about equally (1× vs 2.2× inflation), so at least their relative sizes were preserved — even if both were drawn at the wrong absolute scale.
Mongolia fits 6× into Europe.