Install `pv` and put it between input / output only dd commands.

*Note*: you cannot use it when you already started `dd`.

###From the package description:

> pv - Pipe Viewer - is a terminal-based tool for monitoring the
> progress of data through a pipeline. It can be inserted into any
> normal pipeline between two processes to give a visual indication of
> how quickly data is passing through, how long it has taken, how near
> to completion it is, and an estimate of how long it will be until
> completion.

###Installation

    sudo apt-get install pv

###Example

    dd if=/dev/urandom | pv | dd of=/dev/null

###Output

    1,74MB 0:00:09 [ 198kB/s] [      <=>                               ]

You could specify the approximate size with the `--size` if you want a time estimation.

###Other uses

You can also use it to output to stdout:

    pv /home/user/bigfile.iso | md5sum

###Output

    50,2MB 0:00:06 [8,66MB/s] [=======>         ] 49% ETA 0:00:06

Note that in this case, `pv` recognizes the size automatically.