Over the years researchers have proposed and developed models for extraction of digital evidence in mobile devices but little has been done on standardization of these models hence leading to inconsistencies in the extraction process used since most of the models developed cater for specific needs or a group of interest. In this paper we propose a metric for specification of a consistent digital forensic evidence extraction process in mobile devices to address the inconsistencies in existing digital forensic evidence extraction models for mobile devices running on android, windows, Apple iOS and Blackberry operating system. The proposed metric is aligned with Digital forensic principles and standard operating procedures (SOP), forensic and legal requirements, digital evidence quality, extraction tools and digital evidence legal admissibility. The metric has an integration of several factors such as policy, extraction method, nature of data, device factors, forensic extraction tools and forensic documentation process with consideration of the mobile device operating systems platform. This metric is relevant to law enforcement officers and digital forensic practitioners as well forensic extraction tool developers.