Actually, the real point is that the average person doesn't need engineering precision which is my original point. Whether it's 60sec or 65sec to xfer a file doesn't matter to them. Engineers always like to argue precision to justify complexity and lose sight of the larger picture (eg. consumers/majority matter).

btw- how does expression it in bits v/s bytes help you with your desired calculations?

For example, the TCP throughput equation which can be expressed by the following http://www.mathcs.emory.edu/~cheung/Courses/558/Syllabus/07-... (depending on your degree of accuracy).