I am currently reading a book ("The Mortal Sea" by W. Bolster) which discusses the fishing conditions in Europe and North America. Bolster claims that in the 1500s and 1600s there were no standard units of measurements, and that as a result people often resorted to analogies. Specifically he is discussing a quote by John Mason about Newfoundland- "the most admirable is the Sea, so diversified with several sorts of Fishes abounding therein, the consideration whereof is readie to swallow up and drown my senses not being able to comprehend the riches thereof." Bolster states that perhaps this was not a hyperbole, as the abundance of sea-life in Newfoundland exceeded Mason's ability to think of an ample comparison. This is followed by the assertion that the exact number and weight of fish caught was not measured as it was not considered useful at the time. How true are these statements?
This is a ridiculous claim, and easily proven false if Bolster is making a blanket statement about all of Europe. Perhaps this was true in certain regions, such as Newfoundland and other fishing communities, but even then I find that difficult to believe. As far as standard weights and measures in other parts of Europe go, the many trade manuals of the fourteenth century indicate a number of regionalized standard measurements as well as rates of conversion.
Here's a translation of an excerpt from the Pegolotti manual. It's not as detailed as the whole thing, but you get an idea.
https://depts.washington.edu/silkroad/texts/pegol.html
Here's the whole thing if you're interested. I believe there are some notes at the end that give weight comparisons, and could help you convert those numbers into modern weights if you're really interested. I had to make some conversions of exact weights of grain for my dissertation prospectus.
http://www.medievalacademy.org/resource/resmgr/maa_books_online/evans_0024.htm#hd_ma0024_head_001.
Although there was a plurality of systems of weights and measures in place in the fourteenth century, it seems that the Venetian and Genoese systems were the most prominent depending on what part of the Mediterranean you were in. By the 1500's, however, one would have to assume that the Venetian system was prevalent, but the British and French merchants that began to do business with the Ottomans would have brought their own systems.
While the fishing villages described in The Mortal Sea may not have needed standard weights and measurements, the contemporary systems in place in the Mediterranean would have been very different.