[wardbradt]

It depends on the application/ use case, but typically they are small. For a strategy my team is currently developing, each message contains 2-4 dynamic data points. Messages also include a minimal header[1] and "trailer" (checksum). The header includes data about body length, message type, etc. Messages in my use case are about 64 bytes, but my use case is on the lesser end in terms of payload size. I'd say a typical payload is ~64 to 128 bytes.

It is probably important to mention that some firms communicate with exchanges/ brokers via a direct connection rather than the internet.

[1] https://btobits.com/fixopaedia/fixdic44/block_Standard_Messa...