Body size is a crucial life history parameter for an organism. Therefore, mass estimation for fossil species is important for many kinds of analyses. Several attempts have been made to yield equations applicable to dinosaurs. In this paper, we offer bi- and multivariate equations based on log transformed appendicular skeleton data from a sample of 16 theropods which were known from reasonably complete skeletal remains, and spanning a wide size range. Body masses of the included taxa had been found by displacement methods of scale models, based on measurements taken directly on the mounted skeletons. Seven of the bivariate regression analyses resulted in correlation coefficients equal to or above 0.975 and femoral length was the best available measurement (r=0.995; standard error of the estimate (%SEE)=19.26; percent prediction error ({\rm %PE) = 13.81} ). Also, 32 multivariate analyses yielded equations with high correlation coefficients (r>0.990) and low standard errors.