The MATHEMATICAL maximum transfer of 1Mbps full duplex (megabit per second, or Mb/s) is roughly 320 gigabytes per month in each direction (320GB in and 320GB out). This is calculated from the number of seconds in a 30-day month multiplied by the number of bits in a megabit.
Seconds in a month (60 seconds in a minute * 60 minutes an hour * 24 hours a day * 30 days a month) or 2592000 * 1048576 bits = 2717908992000 bits or 316.40625 gigabytes in and out equals a total of 632 gigabytes. In and out mean the incoming and outgoing transfer of a port. Each way can use 316GB of transfer, with the “outgoing” transfer being the most predominantly used.
The REAL WORLD USAGE value of 1Mbps is much less than the mathematical value. Since it is based on several variables, it is impossible to state what your real use could be.
When calculating Mbps from GB, never use the 316GB value as it will almost never be anywhere near accurate. Always consider a conservative number such as 150-200GB per 1mbps outbound, as this is what the typical end-user’s usage of bandwidth equates to.