This is how the stores categorize releases:
SINGLE:
1-3 tracks (except when one of the tracks is over 10 minutes long, then it's 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 (or when the accumulated runtime of all the tracks is over 30 minutes)
The rules differ a bit on Spotify:
Single/EP: The release is under 30 minutes, and the release has 5 or fewer tracks.
Album: 6 tracks or more