Semiconductor microcavities have great potential for quantum information science, quantum optics, and quantum sensing. Researchers designing devices based on these microcavities could benefit from having accurate figures of merit to guide their design and enhance the entanglement latency and strength of their devices. This article presents a closed formula for computing the exciton-photon concurrence in semiconductor microcavities. The formula is tailored for the ultralow density limit of both excitons and photons, allowing a better understanding of the entanglement properties in this regime.The closed formula allows for accurate and easy quantification of the exciton-photon coupling strength in terms of the parameters of the system like the couplings, frequencies, and linewidths, which has applications in quantum optics and quantum information science. The presented formulas can be used in rational microcavity design for various applications, such as single-photon sources, quantum light sources, and optoelectronic devices. This contributes to the systematic design and control of entanglement properties of quantum devices tailored for specific tasks in quantum information science, quantum optics, and quantum sensing.In summary, this work represents a valuable contribution to both practical applications and fundamental research in the fields of nanostructures, quantum optics, and quantum information science.