Asia is clearly the larger of the two: about 44,580,000 km² km² against 24,710,000 km² km², roughly 1.8× at true size. Drag one onto the other on the map above to feel the gap.
The old Mercator map treated both about equally (1× vs 1× inflation), so at least their relative sizes were preserved — even if both were drawn at the wrong absolute scale.
North America fits 1× into Asia.