Leafsoft Password Strength Meter is a tool for checking the strength of a password. It checks not just the length of a password but also its complexity. The algorithm used to determine password strength takes into account the varieties of characters used (lowercase, uppercase, numerical, special characters) and similarity to the username (if specified).
Passwords of lower than 50% strength are not recommended for use. Passwords of between 50% and 80% are strong enough for most purposes, and those beyond 80% are very secure for any application.