A message isn't sent in it's entirety - it's broken up into little packets of data, each one going to a specific destination. But how little are those packets? I can't find the answer on Google.
closed as too broad by Daniel B, Canadian Luke, DavidPostill♦, Scott, LPChip Sep 2 '15 at 11:53
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The average size of the packet would depend on the application. @DrZoo is largely right - a typical packet on the internet is 1476 - 1500 bytes, however bigger or smaller packets are possible.
This answer does not take into account when a small amount of data is sent in a packet - for example in a chat session. Also, when downloading something like a webpage, the last packet relating to each connection would not be full. I'd guess the average packet for TCP is somewhere in the region of 1400 bytes - but if you are talking about tcp/ip its a lot lower - things like games, voip etc often use a lot of very small packets.