After you run some backups you will start to see the Deduplication Factor increase. For example, you might see 10.34. This means that without deduplication, you would need 10.34x more storage space to backup the same data. In other terms, if you had 10 gigabytes of data, you would need 100 gigabytes of storage space without deduplication.
You can figure this out with the formula:
deduplication = original data size / backed up data size