Page Life Expectancy

Hi,

I checked  PLE value using "sys.dm_os_performance_counters" page life expectancy value is showing as 1650.But when i calculated manually The value coming is 823. The formula used for calculation is ( Buffer pool memory in GB / 4 ) x 300

Which one is correct?

object_name                                              counter_name       cntr_value      cntr_type
MSSQL$TESTHQL00V:Buffer Manager              Page life expectancy        1650                 65792                                                                          

Regards,

Vignesh