size in bytes of a table?

I'd like to present some statistics on our database tables,
showing the number of rows and approximate amount of data
in bytes, e.g. something like this from one of our other
databases:

tasks  (546916 Kb,62018 rows)

Exact numbers don't matter, I just want to present a feel
for the amount of data we have.

Thanks!
Mark

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Mark Harrison
Pixar Animation Studios