In the start menu, open "Settings" and go to "Network and Internet". After clicking on "data usage" on the left side, you will see how much your data usage has been over the past 30 days. After clicking on "Show usage details", Windows breaks down the transferred data volume by application. You can also switch between Ethernet and WLAN via the drop-down menu above. By clicking on "Reset usage statistics" you can reset the counter to zero. This is best done once you have connected to the foreign, volume-limited Wi-Fi.
In Windows you can check on the way, which data volume you have loaded on your computer in the past few days.