International security evaluation metrics are too general and not focused on evaluating security models implemented using Public Key Infrastructure (PKI). This study was conducted to develop the metric for evaluating security models based on implementation of PKI by using insights from literature. Literature review was done based on inclusion and exclusion criteria. The developed metric was tested using ranking attributes and ranking scales. The results reveal that the developed metric is applicable for evaluating security models based on implementation of PKI. This is verified by the tabular results indicating evaluation of selected security models based on implementation of PKI by using ranking attributes and ranking scales. This study contributes to the body of knowledge a metric for evaluating security models based on implementation of PKI.