Background: One of the major challenges of primary health care (PHC) in developing countries is supplying the growing needs of the populations with sufficient and skilled health workers. In this context, use of a simple and relevant workforce planning method such as Workload Indicators of Staffing Need (WISN) could help authorities allocate adequate number of professionals to health centers to meet the health needs of target populations. Methods: This was a descriptive-analytical study, and WISN methodology was used at 48 Comprehensive Health Centers (CHC) located in the northwest of Tehran, in 2022. The present study was conducted in 7 steps and included measures such as the available work Stime, initial and final required manpower, extracurricular activities and their coefficients, standard work activity and workload, and scheduling activities. Results: According to the collected data, the total number of health care workers needed for the covered population was calculated to be approximately 1018 people, and the ratio of available manpower to the required manpower was reported as 24%; this indicated a 76% difference in the number of health care providers regarding the implementation of complete service package. Conclusion: The results of the research showed that if all the referrals are made through network, the network would likely have a shortage of human resources. Although the standard workload in most cases is lower than anticipated based on the reviewed performance regarding the health care provided, this can be caused by not going to the center to receive services, going to the private sector, and also not knowing about the services that can be provided.