The site, called Know My App, also provides some tips on how to be more frugal with your phone or tablet. The most common sense rule is to switch from cellular service to Wi-Fi whenever a secure Wi-Fi connection is available. Another good tip is to make sure that your apps don't update unless you're on a secure Wi-Fi network. Also, it is a good idea to minimize apps not in use so that they aren't running in the background. And you should uninstall any apps that you are not using.
KnowMyApp.org will give you an estimate on how much data you will burn installing, initializing and running an app and will even show how much data a particular app will burn running in the background. Right now, the site has information for the top 50 paid and free apps on iOS and Android and plans on adding more each month. Developers are invited to submit their apps for testing.
source: KnowMyApp via PCWorld, Engadget