Video games and the 21st century's strictly organized standing armies have conditioned us to perceive a military force in terms of its strict organizational structure, and to perceive a soldier in terms of his armaments. I understand, however, that not that long ago, armies were raised in many places in the form of a levy. How would a commander take inventory of such a disorganized, irregular force?
DISCLAIMER: I understand that many people on /r/AskHistorians don't like the word "feudalism" so I think it is appropriate to define a "feudal levy". I am defining a feudal levy as an irregular army raised ad hoc by delegating military service down a hierarchical chain of responsibilities. Examples of systems I would consider to be feudal are the Mughal Mansabdar system and the Ottoman Timariot system.
An assessment of the forces at their disposal would only be possible by surveying and counting what men you had. A levy was rarely divided into neatly organized units, but a unit from town "X" could be assigned to a certain position, and command given to the most experienced/well liked by the supreme commander. Levies would also vary greatly from place to place: a county or town would usually be required to field a certain number of units based on the percieved value of a type of soldier and the size/wealth of his area. A knight could typically be worth 2 men-at-arms, or several bowmen. Knights also brought their own band of men with them: if a lord had count of his knights, he could expect each "lance" to be a handful of men, and counting the number of knights would often be an estimate of how many times larger the force would be. Many lords on bad terms with a king would only field the bare minimum required of him.
Again, counting the men levied was usually the way to go. You never knew exactly how many men you had with you, and most men of some wealth were expected to provide their own arms unless they were directly in the service of a lord or knight, as in part of their retinue.