Reflected spectral radiance measured by the Multi-angle Imaging SpectroRadiometer (MISR) on the Terra satellite has been analyzed to determine the fraction of global cloudiness that appears to be spatially homogeneous over regions of various sizes. We exclude scenes with reflectivities less than 0.2 and high latitudes to avoid snow and ice. About 1.4 ¿ 0.3%, or 1 in 70, of 8.8 km cloudy regions measured at 275 m have a range of reflectivities less than ¿5% of the central reflectivity value of the region. This pass rate changes slightly with viewing angle, and is sensitive to the size of the test window, rising to 11% for 1.1 km regions. The pass rate rises to a value of 2.3 ¿ 0.5% for 8.8 km regions if the measurement resolution is degraded to 1100 m. For the purposes of this study global cloudiness is limited to mid-morning clouds.