M = Million
K = 1000
Lower case K, when talking about data rates, is a typo, as it should be the upper case.
Where case matters in these abbreviations generally is for the B
lower case b = bits
upper case B = Bytes
Usually, because of coding, the Bytes per second on a link is NOT bps/8. It used to be bps/10 (allowing for space and parity) on a traditional serial line, but that is no longer universally true.
#b/s is just another way of writing #bps
Since you're talking about bits per second, there should be no need for non-decimal conversions. Unlike bytes of data (usually when talking about RAM or HDD capacity), bitrates are not divided on binary K boundaries (1024), so you just convert by power of ten.
So, 0.53Mb/s = 0.53Mbps = 530Kbps
