The formation of epitaxial graphene on SiC is monitored in situ using low-energy electron diffraction (LEED). The possibility of using LEED as an in situ thickness monitor of the graphene is examined. The ratio of primary diffraction spot intensities for graphene compared to SiC is measured for a series of samples of known graphene thickness (determined using low-energy electron microscopy). It is found that this ratio is effective for determining graphene thicknesses in the range of 1-3 ML. Effects of a distribution of graphene thicknesses on this method of thickness determination are considered. (C) 2010 American Vacuum Society. [DOI: 10.1116/1.3301621]