How Much Cellular Data Does Pokemon Go Use?
It has been estimated that Pokemon Go uses 5-10MB of data per hour. For some perspective, streaming an HD video uses around 350MB of cellular data each hour. In general, Pokemon Go is more of a drain on your iPhone battery than your data plan.
Based on the 5-10MB of data per hour estimate, if Pokemon Go used a full 10MB per hour and you played for three hours a day, you would exhaust about 900MB (or 0.9GB) of data over the course of a month.