These were the smallest landholders, generally overseeing between 20 and 200 peasants and their work, though some esteemed knights were appointed to rule over towns due to the fact they presented very little in the way of a social threat to their Lord's power.
Generic title for tens of thousands of minor landholders (Baronets, ect.) who had a few knights serving under them, and the lowest rank of the peerage. Usually had between 1 and 20 knights under them, generally unlanded knights who were used for battle only.
First "Real" rank of the peerage. Often considered the lowest rank of the nobility, these large landowners were also the first rank likely to have a keep that was anything more than a fancy name for a mansion. They were generally given dominon over between 2 and 25 minor lords and their retainers.
A rank with some controversy, Viscount is probably more accurately called "Extremely powerful Baron." Later in the Middle Ages this was formalized into Viscount status and they were ranked above Barons but below Counts. They generally can call upon 3 to 30 Barons, though the upper end of that scale leans more towards Count status.
Very large and esteemed landholder, generally had 2 to 3 Viscounts under them if applicable and dozens of Barons. Some counts do not answer to a Duke but directly to the King himself, though this is not common. Very powerful, lowest rank capable of conducting a real war (minor one, but still) by itself.
Second highest ranked title after King. Largest landholders after the King, usually with between 2 and 8 Counts answering to them along with a multitude of Barons, Lords, and landed Knights. Extremely influential and powerful and as a group often shaped kingdom policy more than the King himself.
Usually the largest landholder with the richest provinces under his direct rule, but not always.