The solubility product for the hydroxide of a metal ion, M, is usually defined,  as follows:
However, general-purpose computer programs are designed to use hydrogen ion concentrations with the alternative definitions.
For hydroxides, solubility products are often given in a modified form, K*, using hydrogen ion concentration in place of hydroxide ion concentration. The two values are related by the self-ionization constant for water, K.
For example, at ambient temperature, for calcium hydroxide, Ca(OH), lg K is ca. −5 and lg K* ≈ −5 + 2 × 14 ≈ 23.