We calibrate a subgrain-size piezometer using electron backscatter diffraction (EBSD) data collected from experimentally deformed samples of olivine and quartz. Systematic analyses of angular and spatial resolution test the suitability of each dataset for inclusion in calibration of the subgrain-size piezometer. To identify subgrain boundaries, we consider a range of critical misorientation angles and conclude that a 1° threshold provides the optimal piezometric calibration. The mean line-intercept length, equivalent to the subgrain-size, is found to be inversely proportional to the von Mises equivalent stress for datasets both with and without the Holyoke and Kronenberg (2010) correction. These new piezometers provide stress estimates from EBSD analyses of polymineralic rocks without the need to discriminate between relict and recrystallised grains and therefore greatly increase the range of rocks that may be used to constrain geodynamic models.