Thought of a new tub

i was at home depot today and noticed an off brand of tubs it didnt say what size it was, so i got the size it is 21in long 16in wide 7in deep is that too small or just right for an adult ball to be in???

That is fine for an adult male for sure. It would also be fine for smaller adult females. But anything bigger than that (for me) goes in a large tub. (41qt)
-Steven
PS The 27/28 sterilites are 23X17X6 so comapred to your tubs are just a touch bigger.