Install iostat, then run (in a second command window) the command
iostat -k -x 2
Change the 2 for any refresh rate, no matter the refresh rate, you will get the KBytes per seconed both read and write for both disks involved in the copy. You will also get the total copied for the period of time between refresh, so always take note of the (per second) sign in kB_read/s and kB_wrtn/s.
To recap, kB_read/s and kB_wrtn/s are not affected by the interval you set, while kB_read/s and kB_wrtn/s. are affected (they are the result of multiplying the speed (/s) by the interval you set
The K stands for KiloBytes (the default is blocks), you can also use m for megabytes
the X stands for Extended statistics (You probably dont need it for this particular purpose)
We are doing the above because CP and MV do NOT provide means of monitoring transfer rate.
Some other solutions like pv and rsync do, but would you want to get into all of this every time you want to copy a file or folder ?
Anyway, here is a rundown of all the ways that can allow you to monitor speed when you copy or move
(I will come back to this in a bit.