Pesticides are widely used to control undesirable organisms in agriculture and in other parts of society. As well as controlling pests these chemicals may have harmful effects on non-target organisms including humans. Because of these possible harmful effects, residues from pesticides applied to food crops are permitted to be present in the harvested crop and in processed products made from that crop only at or below a certain fraction of the weight of the harvested crop. In order to make safety findings, EPA conducts dietary risk assessments for pesticides. These risk assessments may depend, in part, on estimates of the percent of a crop that is treated with a particular pesticide. Analysts within OPP (Office of Pesticide Programs) provide estimates of percent crop treated (PCT) to support these assessments. The purpose of this paper is to describe the present methods for estimating PCT, as background information to support OPP's proposed refinements in calculating PCT. This paper will first briefly discuss the estimation of dietary pesticide exposure, one of several possible routes of pesticide exposure. The various types of data used in this estimation will be covered. This paper then discusses various aspects of the determination of total individual pesticide exposure to show how percent crop treated data contributes to the determination of the 'reasonable certainty' criteria. Analysts' estimates of percent crop treated data are used by dietary risk assessors in OPP. OPP uses a number of data sources and computer algorithms to develop these estimates. The present methods of estimating percent crop treated will be discussed, and this discussion is intended to help in forming improvements in these methods. One expected improvement will be a new algorithm that will aid in predicting average future percent crop treated with a pesticide, as well as possible maximum percent crop treated.