A combinatorial batch code was defined by Paterson, Stinson and Wei as a purely combinatorial description of batch codes, which were first introduced by Ishai, Kushilevitz, Ostrovsky and Sahai. It is a system consisting of subsets of an -element set such that any distinct elements can be retrieved by reading at most one (or in general, ) elements from each subset and the number of total elements in subsets is . For given parameters , the goal is to determine the minimum , denoted by . So far, for and , precise values of have not been established except for some special parameters. In this paper, we determine the for , and give a bound on for , which is tight for some .