We attempt to understand why volcanic ash grains found 100s of km from their source volcanoes (cryptotephra), which are typically 20–125 microns in length, are much larger than the size distributions measured by satellite remote sensing, which are centred at less than 10 microns. Our observations and models show that cryptotephra-sized grains are to be expected in distal plumes. Retrievals of effective radius made on simulated satellite images are shown to be biased toward smaller values.