The application of hydrostatic pressure allows the precise tuning of atomic separations, which control electronic structure and virtually all the interatomic interactions that determine materials¿ properties. With pressure tuning, properties can often be more rapidly and cleanly optimised than with chemical tuning, which necessitates the exploratory synthesis of a large number of different materials. The aim of this proposal is to explore both chemical and physical pressure in a family of perovskites and use the structural changes observed to quantify the chemical pressure generated by changing lanthanide ion in terms of an effective hydrostatic pressure. Ultimately we see this work as an important first step towards a goal of targeting desirable properties in functional materials by tuning the chemical pressure.