Contact electrification (CE) has been one of the most important physical phenomena in surface science for more than 2600 years. Although a large number of experiments have been conducted to detect CE and theories about electron, ion, and material transfer have been proposed, the mechanism of CE remains a subject of ongoing debate and continues to stimulate the interest of scientists. A key issue in charge transfer research is how to accurately measure charge transfer in various situations. Developments in charge transfer measurements have consistently led to a deeper understanding of CE. In this review, we explore the field of CE with a focus on methods for measuring charge transfer. And a quantitative materials database serves as a valuable resource for systematically analyzing the relationship between triboelectrification and the properties of different materials. Numerous approaches have been developed to assess and measure the triboelectric properties of materials. This chapter focuses on the methods used to characterize the triboelectric charge density of various materials. These quantitative triboelectric charge densities could act as a benchmark reference for advancing the use of triboelectrification in energy harvesting and self-powered sensing applications.