With constant use, SD channels (regular quality) can use up to 1.3 GB of data per hour. In HD mode, channels can draw up to 2.2 GB per hour. These are only guidelines.
In our iOS app you have the possibility to change the bitrate from high to low (especially recommended when using Zattoo in mobile network). You will find the option in Settings.
At a reduced bit rate (option available in the app settings) we limit the data use up to 900 kbps. As such the data use is around 400 MB/h per hour