This document is a product of efforts by the Agency to develop and promote biologically based and harmonized approaches for all toxicological endpoints used in human health risk assessments. EPA risk assessors routinely use body weight (BW) as the basis for scaling toxicity data from animal models for human health risk assessments. However, the Agency has used BW(1/1) for non-cancer endpoints and, at various times BW(2/3) or BW(3/4) for cancer endpoints to normalize dose across species. This document promotes the use of BW(3/4) as a default method to convert data between species for both categories of endpoints. A hierarchy of methods for interspecies scaling is presented along with the rationale for selection of the scaling factor and guidance on how to conduct the conversion. EPA endorses a hierarchy of approaches to derive human equivalent oral exposures from data from laboratory animal species, with the preferred approach being physiologically-based toxicokinetic modeling.