The cp command is not really good with that, there are some ways to do it, but unnecessarily complicated.
The best option is to use rsync instead:
rsync --progress source destination
It will show you something like this:
3885367296 0% 38.37MB/s 13:02:45
Where the first column is the number of copied bytes, the second one is the percentage of completion, the third is the copy speed and the last is the remaining time.