Horsrud-Vp (Horsrud, 2001)

UCS = 2.12e⁹ ´ Dt^–2.93

where

-2.93 is a non-dimensional constant.

2.12 is in psi.

This equation is based on laboratory measurements on North Sea shales. The rocks were mainly high-porosity Tertiary shales with very few compacted and well-consolidated samples. When the equation is applied to the source data, the uncertainty is estimated to be up to 50% for weak samples (UCS < 1,500 psi) and between 10 to 20% for stronger samples (UCS > 7,000 psi). This equation is selected as the default for shale.