Closer than most people guess: Algeria (2,322,788 km² km²) is only about 21%% larger than Saudi Arabia (1,925,871 km² km²).
Algeria sits in Africa, Saudi Arabia in Asia. On the old Mercator map the latitude gap distorted how large each felt beside the other; at true size the answer is simply 1.2×.
The old Mercator map treated both about equally (1.3× vs 1.2× inflation), so at least their relative sizes were preserved — even if both were drawn at the wrong absolute scale.
Saudi Arabia fits 1× into Algeria.