Eleven granulations of a common filler (lactose) and three granulations of a high dosage drug (dipentum) were produced by wet granulation with polyvinylpyrrolidone as binder in a high shear mixer. The agglomeration process was varied to produce granulations with varying granule porosity. The size fraction 500–710 μm was separated and characterised on binder content (lactose granulations), granule porosity and friability. The granule fragmentation during compaction was evaluated by measurements of the air permeability of the tablets. Finally, the diametral compression strength of tablets compacted from unlubricated granulations and lactose granulations lubricated with 0.5% by weight magnesium stearate at 150 MPa was measured. The results showed that the degree of granule fragmentation during compaction was related to the granule porosity before compaction. A granulation with a higher porosity had a higher fragmentation propensity, as evaluated by the permeametry measurements, and the tablet strength was less affected by magnesium stearate addition. The tablet strength correlated well with the degree of fragmentation, i.e. a granulation with higher degree of fragmentation gave tablets of a higher mechanical strength. These observations suggest that variations in compactibility, when the same formulation is wet granulated under different process conditions, can be explained by variations in granule porosity.