The Hadoop in Real World team has two methods of finding free space in HDFS:
It is a quite common need to find the available free space in HDFS. There are a couple of ways to find this information.
If you are using a cluster manager like Ambari or Cloudera Manager then you can go to the HDFS service and see this information in the summary section.
Click through for an image of that, as well as a command line technique.