Africa dwarfs Mauritania: about 30,370,000 km² km² against 1,038,352 km² km². At true size Africa is about 29.2× larger — the whole of Mauritania fits into Africa roughly 29 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 29× into Africa.