On an Android smartphone you can get a close estimation on usage from the phone itself.
Touch settings, then touch network and internet,
This should be the screen that then allows you to do any of the following,
Turn on wifi
Turn on Hotspot
and one spot should show data usage. If you touch that you can set the dates for the data cycle to whatever ones you wish, and then monitor the amount used from this screen whenever you wish.
Just use the hotspot for your e mail and news reading a few days and you should have a good idea.
The phones measured data may be a little off as compared to the carrier, but they usually are withing 5% or so.