Calcite deformed by high temperature creep develops a heterogeneous microstructure consisting of deformed and recrystallised grains. The deformed grains either contain homogeneously distributed subgrains of similar size, or heterogeneously distributed small subgrains at grain boundaries (mantle subgrains) and relatively large subgrains in the core of grains (core subgrains). This paper demonstrates a method using electron backscattered diffraction (EBSD) to distinguish between the different types of grains and subgrains and to measure their sizes separately. In geological materials the average subgrain size, regardless of the subgrain type, is often used to estimate the deformation stress. However, this paper shows that mantle and core subgrain types only show a weak or no stress dependence.