Soil weight is referred to as soil bulk density.
Density is the mass of material contained within a given volume.
This is the idea that a given size of box may be heavy or light, depending upon what kind of material it contains. If the box were filled with pinewood, it would be light when compared to having it filled with lead. The volume of the soil can be determined by pouring the soil into a graduated cylinder and measuring the volume that it occupies. The problem with this procedure is that structural aggregates may be crushed or compacted once they are removed from the soil and placed into the cylinder. A better procedure is one in which the aggregates could be removed from the soil and frozen exactly the way they were in the soil.