Over the past two decades, test data compression has become a de facto technology used in large industrial designs to reduce the overall test cost. During DFT planning, it is very important to understand the impact of using different numbers of input/output channels on test coverage, test cycles, and test data volume. In this paper, an efficient method to estimate the test data volume with different input channel counts using the Embedded Deterministic Test (EDT) compression technology is proposed. The results can then be used to quickly determine the scan configuration that results in the least or near least test data volume. With this method, the total ATPG run time can be reduced by a factor of more than 10X compared to the currently used trial-and-error method.