GMI-Jizba-Phi (Jizba, 1991)

UCS = 4697Φ^–0.466

where:

4697 is in psi.

Analyzed by Jizba (Stanford PhD thesis, 1991). The sample data was derived from low to medium porosity, low permeability, consolidated sandstones (1% < phi < 18%); therefore, its applicability is limited to similar rocks. This equation is based on laboratory test data from Travis Peak, Texas shaley sandstones.