I would divide mass by volume to find the overall density. I would then divide the overall density by the actual density of the material, to find the packing density.
You may want to consider measuring a tap density, which will give you a more accurate estimate of the powder packing density. A procedure would be to measure 100 cc of your powder into a graduate cylinder, then vibrate the cylinder for several minutes, and then record the volume and mass and divide to find your density.