Although Viber is free to use but it doesn't mean you shouldn't pay for the Viber data usage when making voice or video calls, receiving or sending photos and videos and other type of contents. To find out how much data Viber has used over a certain period on both mobile data and Wi-Fi networks on Android devices, do as follow:
1. Open Settings and tap the More option under the Wireless & Network settings
2. Tap to open the Data Usage settings (On some devices, this option is right on the main page of the Settings and on some others you may have to jump to the Connection tab)
3. Tap the 3dot icon on the top right and make sure the "Show Wi-Fi usage" option is makred
4. Now, tap the Data usage cycle option and specify the period you'd like to see Viber data usage in
5. Scroll down, find the Viber and see the data usage over the given cycle
**Note that, the default view is for Mobile Data Usage and to check the Viber data usage over wireless networks, you should swipe to the Wi-Fi tab