I do not have an exact answer, however, the virus RNA can be produced wrapped in a nucleoprotein then packaged as a viron. I believe the cell size governs the capacity /number of virons. The virus produces 9 different RNA's particles however can package between 7-12 RNA particles. I believe a perfect Viron (infectious virus) requires 9 different RNA's that are packaged into a viron - the number of viruses per cell could range between 100 - 1000.