A count of one gives the number of yards per pound, but it depends on the yarn. See the table below. 300 Cotton 840 Spun Silk 840 Worsted wool is nothing to do with worsted weight yarn. Worsted wool is wool which is carded and combed so that all the fibres are parallel. Woolen measure or Yorkshire wool is carded but not combed, so is a little rougher.
Worsted wool is usually very fine and used for suits and fine fabric.
Hand knitting yarn is usually woolen type yarn. This will be in the DK to worsted weight range. Finally, you have to remember that hand knitting yarns vary a lot in weight per yard, from brand to brand, and type to type. For example a superwash wool is heavier than a regular wool. With this in mind we can produce a table for various counts of wool.