Connection speeds are quoted in bits per second (a 500 Mbps plan), while browsers and download managers show bytes per second (62.5 MB/s). Since a byte is 8 bits, the download figure is always one eighth of the line rate, before protocol overhead takes another few percent. All prefixes here are decimal, as used by ISPs and the IEEE: 1 Mbps is 1,000,000 bits per second.
Use the converter above for any pair. The most searched conversion, Mbps to MB/s, has its own page with worked examples and a table of common plan speeds.