We size air compressors around the volume and pressure requirements of the facility in question.  In many instances, we’re working off an existing system, which allows us a starting point in future sizing.  In other instances, we can calculate air requirements around the specific equipment running in a given facility and sizing around those parameters.  To go even further, we can data log an existing compressor system by installing loggers on a compressor control panel that actively tracks real time amp draw of the compressor against system pressure to calculate what kind of capacity the compressor is running at in order to maintain system pressure.  This information will allow us to size a new compressor as accurately as possible.