There are 17,576 letter only and 46,656 letter and number 3-word variations.
So I'd say it'll range from 10M (random, no meaning, numbers included) to 10B (meaning).
e.g:
X53 = 10M
FHV = 20M
XXD = 200M (X + laughing face)
XXX = 1-5B
DED = 2-4B
DAD = 6-10B
LOL = 10B+