I was talking about length of musical content - not file size.
MP3 compression is around 11:1.
Most music CDs - based on a quick sample of my collection - seem to clock in around the 45 - 50 minute mark. Call it 500 MB.
So, a 500MB album is compressed to a 45MB MP3.
32000 / 45 is ~700 CDs worth of music.

That is, if you were to take the top 700 albums of all time and turn them into MP3s, they would fit onto a 32GB microSD card.

Sorry for the confusion.