I have a very old pound cake recipe that calls for a “round” of butter.  How much is that?  I have no idea. 
A round of bread or butter seems to be a term that is used by some English speakers, but I'm not sure where from. I'm not sure what equivalent measurement it has, if it even has an exact measurement, but I think it has the idea of an entire piece of butter. Survey of English Dialects:   Slices of bread alongside a round of butter and a hillock of sea or river salt was neatly presented on a plate deliberately pottered with bits missing.      from a restaurant review     The butter is weighed into balls either the size of those sweet tiny pats (used in restaurants and on airplanes), the most popular round 220 g block (not sure if it is called a block if it is round…) or the sleek rectangular blocks (very sexy in their shiny silver wrapping, with the label stamp-pressed on) for restaurant use.    Pepe is making a special round of butter for our breakfast   from http://mondaymorningcookingclub.com.au  