ISP's often provide their speeds in "Megabits per second", since "10 Mbps" is a larger number than "1,25 MBps", and people don't notice the small B in Mbps.
So heres a small writeup to understand your internet speeds better.
Mbps = Megabit per second.
MBps = MegaByte per second.
Note the large B and Byte vs Bit.
1 Byte is 8 Bits, so the conversion from one to the other is pretty simple. Divide Mbps by 8 to get MBps, and mutiply MBps by 8 to get Mbps.
Megabyte is useful cause we often use Bytes to measure filesizes. So lets say youre downloading a 20 gigabyte file at 1.25 MegaByte per second;
20*1000 = 20,000 (turn gigabyte into megabyte)
20,000 / 1,25 = 16,000 (divide size by download speed, giving you seconds)
16,000 / 60 / 60 = 4,4 (divide seconds by 60 to give minutes and 60 again to give hours.)
so 20 gigs should take aprox 4-5 hours at 1.25 MBps
Also, you used MiB/s, which is Mebibyte per second, which is just the IEC name for megabyte.
Just as a last note. Theres decimal and binary multiples of Bytes, so a megabyte can either be 1000^2 Bytes in Decimal, or 1024^2 Bytes in Binary, but MiB is always used for the Binary value.
In a realistic case this is such a small difference that it's often overlooked.