Luckily, you can find out how much actual data you've been using on your Facebook app. How To Find Out How Much Data You Use On Facebook:
If you spend 45 minutes per day using the Facebook app on your smartphone, then you are using just over 2GB of data per month just on Facebook! This doesn't even take into account if you are watching a lot of videos, nor does it take into account the data that the Facebook app consumes in the background of your smartphone even when you don't have the app open. Viewing video content on Facebook uses around 2.6MB per minute, but this can also depend on the quality of video you are watching. Regular usage means browsing through the News Feed, and viewing photos. Regular use of the Facebook app uses around 1.5MB per minute. Right now, using the Facebook app on your smartphone can use a huge chunk of data if you're not careful.
However, the advancement of the capabilities of the Facebook app on your smartphone has led to the Facebook app using more and more data every year.
Facebook is the largest social network in the world, and really great for keeping in touch with your friends and family, watching videos, and discovering news and other articles.