How does sleet differ from snow?
It has a greater density and macro-structure.
Sleet, snow and hail are all forms of solid water precipitation. The differences are in how they are formed in the atmosphere.
Snow is a delicate crystalline structure formed by the nucleation of water into small individual units of frozen water. These fall relatively gently to the ground due to their individual low unit density and mass.
Sleet is directly frozen rain, and is essentially the same mass as a raindrop per unit.
Hail is formed by the recirculation of rain/sleet mixtures in a large storm. The recirculation adds a considerable mass to each individual unit, which are usually roughly spherical in shape. The final weight of a hailstone depends on how long the storm wind recirculation in the cloud can retain the ever-heavier particles.