In live donor liver transplantation, rigorous standardized criteria for matching of liver volume between donor and recipient have prevented graft loss because of size mismatch. In deceased whole liver transplantation, the safe donor–recipient size mismatch range remains unknown. We developed a multivariate survival model (generalized additive model) to estimate hazard risk of body surface area index (BSAi) for 3-year graft survival using data derived from the national registry database between 2005 and 2010. BSAi was calculated by BSA of donor divided by BSA of recipient. 24 509 patients were included in the analysis. Small-for-size (SFS) grafts with BSAi less than 0.78 had a significant impact on graft dysfunction with progressive increase of hazard risk toward the lowest end and a higher incidence of primary graft nonfunction and vascular thrombosis. Large-for-size (LFS) grafts with BSAi greater than 1.24 had a significant impact on graft dysfunction with progressive increase of hazard risk toward the largest end. Our findings suggest that donor grafts with BSAi < 0.78 could be considered ‘SFS’ and donor grafts with BSAi > 1.24 could be considered ‘LFS’, with both extremes resulting in decreased graft survival. Therefore, BSAi > 0.78 and <1.24 appears to be a safe range to avoid adverse outcome associated with size mismatch.