Minimum password length for registration form
You might be looking of Password policy module

Features
Current constraints include:

Complexity constraint

Digit constraint

Letter constraint Letter/Digit

constraint (Alphanumeric)

Length constraint

Uppercase constraint

Lowercase constraint Punctuation constraint

Delay constraint Username

constraint Digit placement constraint

History constraint (checks

hashed password against a collection of users previous hashed

passwords looking for recent duplicates)



Also checkout this Quick demo.