As explained in
What does kbps and mbps mean? an ADSL Broadband connection's speed is displayed in bits-per-second, however a file such as a word document is displayed in Bytes. Bytes are different to bits because they are used to measure space where as bits measure speed. This is why Bits are signified by a small "b" and Bytes displayed as a capital "B".
This leads to some confusion about ADSL Broadband speeds; as often people do not understand why for example a 1.5mbps ADSL Broadband service cannot download a 1.5MB file in a second. In order to help you understand the real speed of your connection try using this simple formula.
8 mega-bits = 1 Mega-Byte
To be more exact try this formula:
(A x 0.1220703125)/1,000,000 = Real Download Speed in KBps or MBps
A = Download speed in bits-per-second (roughly speaking 1mbps =
1,000,000 bits-per-second)
For example:
(12mbps x 0.1220703125)/1,000,000 = 1.46 MBps
or
(12,000,000 x 0.1220703125)/1,000,000 = 1.46484375 MBps
Therefore if you have a 12mbps ADSL Broadband connection you could download at 1.46MBps or a 1.46MB file in one second.