Energy harvesting from multiple sources is a more robust method for powering Internet of Things (IoT) nodes and similar wireless systems compared to harvesting from a single source. This work provides a description of an optimization CAD tool for reconfigurable capacitive DC-DC converters with multiple inputs used for energy-harvesting from multiple sources with varying levels of input power. The tool estimates the theoretical maximum efficiency for each converter configuration, along with the input power condition that achieves this performance. In addition, for given values of the available power from the harvesting sources connected to the DC-DC converter inputs, the proposed CAD tool finds the best converter configuration for that power state of the harvesters.