1. Streaming video content is probably the biggest culprit causing high data usage. Video streaming sites such as Netflix, Amazon Prime, Youtube, and Facebook playing in HD use roughly 3GB of data per hour, per device. If you stream content in ultra HD, the usage will increase again to approximately 7GB per hour, per device. For standard definition, your usage will be lower, at roughly 0.7GB per hour, per device
  2. Downloading large files to your devices. For example, downloading games to PlayStation, Xbox, computers, tablets, and Nintendo Switch. In addition, downloading updates for games can consume large amounts of data.


Activity
Data Consumption Range
Computer/Console Games Downloads. This depends on the game file size itself.  For example, downloading Modern Warfare uses 231GB of data, and would be the largest game to download.  0.4GB-231GB
Game Updates. This depends from game to game, and update to update. It can go from as little as 30Mb to as high as 90GB.  The most common large updates are approximately 30GB.
0.3GB-90GB
Streaming Ultra HD Video. Netflix advises it can use up to 7GB of data per hour per device. This can vary depending on what site or app you stream from.
6Gb-8GB per hour, per device
Streaming HD Video. Netflix advises that it can use up to 3GB per hour, per device. For other video content providers, such as youtube, it also depends on how many frames per second the video has.2.2GB-3.5GB per hour, per device 
Streaming Standard Definition. Netflix advises that it can use up to 0.7GB per hour, per device. Just like the others, it can vary depending on its source, be it Netflix, Youtube, Amazon prime, etc. 0.6GB-0.8GB per hour, per device