In our last MSE data usage poll, 76% of the 4,500 respondents said they use less than 3GB a month, while only 8% of people actually use more than 10GB a month.
If you want to check your usage, our handy Data Calculator in our Cheap Mobile Finder tool can help you. Key in your usage (for when you're not using Wi-Fi) and it'll give you a general idea of how much data you need.