hi,

hehe, it reminds me another joke:
- how do you distinguish between user and programmer?
- it is simple: the user thinks that 1kb contains 1000 bytes and the programmer thinks that 1km is 1024 meters (=

If be serious, you question is over complex out.

First of all, you need to know the bitrate;
then you need to know how much bits it requires to transfer one byte.
For example, bitrate is 9600 boud (bits per second); one byte is transfered with 10 bits (start bit, 8 data bits, stop bit). So at one second it may transmit up to 960 bytes. But! There are another things:
- there is a lag between one byte is transfered and another has been sending. It depends on transfer procedure realization and may be decreased with FIFO buffer or another hardware tricks but you should pay attention on it;
- there are errors on physical layer and so "re-send" scheme is used. It "eats" time and may result to re-sync and put down bitrate. Generally, "packets" is the minimal unit which may be re-called.

So, you never know about time. In my calculations I use formula data_size_bytes * 8/11 for VERY average results!

Regards,
Oleg