We synthesized, characterized, and tested in CO oxidation 13 ABO3 perovskites obtained by a systematic variation of A and B elements (A = La, Pr, Nd, Sm; B = Cr, Mn, Fe, Co) according to rigorous experimental procedures. The activity of these perovskites towards the catalytic CO oxidation cannot be easily correlated the bulk or surface composition or with elemental properties of A or B, but it is well captured by AI. By applying a SISSO analysis, we identified a descriptor for the temperature necessary to achieve 10% conversion ( ? @A ) as an analytical expression. This descriptor contains the key parameters normalized unit-cell volume determined by XRD, the Pauling electronegativity of the A and B elements, and the ionization energy of the B element. The descriptor is of more general validity than the quantities previously proposed as descriptors for activity. It can predict ? @A of 3 additional ABO3 materials and 16 substituted perovskites with the general formula AMn(1-x)(Cu, Fe, Co, Ni, Zn)xO3 (A = La, Pr, Nd) with overall good accuracy. Crucially, this descriptor highlights the so far overlooked role of crystallographic strain, as the normalized unit cell volume is determined by the size of A and B cations as well as by the distortions of the octahedra within the perovskite structure. This work clearly shows that the relationships between the physical properties of perovskites and catalysis are nonlinear and they involve more than one parameter. The approach described in this paper accelerates the development of improved perovskite materials for catalysis by providing insights into the key materials' properties controlling catalysis and thus proposing approaches to the inorganic chemist or materials scientist that are not readily apparent.