Europe dwarfs Mauritania: about 10,180,000 km² km² against 1,038,352 km² km². At true size Europe is about 9.8× larger — the whole of Mauritania fits into Europe roughly 9 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 9× into Europe.