There is no definitive answer to the question of how thin is too thin for a concrete coffee table. The thickness of a concrete coffee table is largely determined by the intended use of the table. For example, a coffee table that will be used for display purposes only can be made much thinner than one that will be used for both display and functional purposes. The weight of the concrete and the type of reinforcement used are also key factors to consider when determining the appropriate thickness for a concrete coffee table.