The distribution of net electric charge in graphene is investigated, using both a constitutive atomic charge-dipole interaction model and an approximate analytical solution to Laplace's equation. These approximations, unlike first-principle calculations, are applicable to graphene sizes that are consistent with experiments. It is found that the analytical model gives a good description of the charge distribution, except for the very edge atoms because of the atomic edge state, which can instead be treated by the numerical model. (C) 2010 Elsevier B. V. All rights reserved.