This is what Amuse follows:
SINGLE: 1-3 tracks (except when one of the tracks is over 10 minutes long, then it is an EP)
EP: 4-6 tracks (except when the accumulated runtime of all the tracks is over 30 minutes, then it should be an album)
ALBUM: 7+ tracks
The rules differ a bit on Spotify: single/EP: The release is under 30 minutes, and the release has five (5) or fewer tracks. Album is 6 tracks or more.