The cumulative efficiency of a filter describes how effective a filter is in retaining solid particles. According to ISO 4572 it is defined by
![f52c3aee45094154f79136c9c60013a008607ca2 abscheidegrad_01.gif](/fileadmin/smc/files/f52c3aee45094154f79136c9c60013a008607ca2.gif)
ε x = filter cumulative efficiency for particles larger than x μm
Nu = number of particles > x μm upstream of the filter
Nd = number of particles > x μm downstream of the filter
The filter cumulative efficiency is normally stated in %. It is related to the value βx from the multipass test.