https://www.econ.berkeley.edu/undergrad/prospective/transfer-students indicates that transfer students intending to declare the economics major need to have at least a 3.0 GPA in previously taken prerequisite courses and a 2.7 GPA in prerequisite courses taken after transfer. The latter courses are one of Economics 100A, 100B, 101A, 101B, and a math or (usually) statistics course.
Students who wish to prepare for PhD study in economics should take the equivalent of Math 53 before transfer in order to be able to take Economics 101A (however, 101B only requires single variable calculus). Such students also tend to choose Economics 141 instead of 140 for econometrics; 141 requires both Math 53 and 54.