Asia dwarfs Mauritania: about 44,580,000 km² km² against 1,038,352 km² km². At true size Asia is about 42.9× larger — the whole of Mauritania fits into Asia roughly 42 times.
The old Mercator map treated both about equally (1× vs 1.1× inflation), so at least their relative sizes were preserved — even if both were drawn at the wrong absolute scale.
Mauritania fits 42× into Asia.