How most of the hosting providers calculate the bandwidth consumption?

Most of the hosting providers calculates bandwidth according to the Total Transfer Method.
This is the measurement of actual data leaving and coming from the server, measured in bytes.

Measurement between providers varies and includes one of the following equations:

* Method 1: IN TRAFFIC + OUT TRAFFIC = TOTAL TRANSFER
* Method 2: IN TRAFFIC = TOTAL TRANSFER
* Method 3: OUT TRAFFIC = TOTAL TRANSFER