Bits vs Bytes
Internet speeds are usually measured in bits per second (bps, Mbps), while file downloads are shown in bytes per second (Bps, MB/s). 1 Byte = 8 bits.
Why does my 100 Mbps connection download at 12.5 MB/s?
Because 100 Megabits / 8 = 12.5 Megabytes per second.