in my modelling, it is advised to have parcels much smaller than cells, so I need to know parcel size.

is (the parcel size)= (number of particles in a parcel)*(particle size)

or it is parcel size=particle size

if it is the first one, I need to know how many particles each parcel contains. using the injection mass provides the mass of all parcels at each time step, so if we do not know number of parcels released in each time step (or number of streams), we cannot have the mass of each parcel (and consequently the number of particles in each parcel and parcel size).