Now that many of us are on metered data plans instead of unlimited, iOS 7 has added a great new feature to help you get handle on your data usage. Head to the Settings app > Cellular and scroll to the bottom. There you’ll see each app and how much cellular data it has used, along with the option to deny any app access to cellular, restricting them to WiFi. If you’re on a limited plan it might be a good idea to disable at least Netflix and Hulu so you don’t accidentally use your data allotment if you aren’t on WiFi.
These stats are not reset at the end of your billing period automatically. Instead, it only resets when you ask using the button at the very end of the list.
If you don’t know what the numbers mean, a 4 GB cell phone plan is about 4,000 MB or about 4,000,000 KB. So in my image below the 90 KB used by my American Express app is about one 44 thousandth of my data limit, hardly cause for alarm.