This document specifies the fundamental characteristics to be measured of a sample of engineered nanoparticles in powder form to determine the size, the chemical content and the surface area. This document also specifies measurement methods for determining each of the characteristics. It is intended to facilitate communication among consumers, regulators and industries with the necessary characteristics. It excludes characteristics that pertain to specific industrial applications of nanoparticles in powder form and detailed measurement protocols, as well as characteristics related to health, safety and environmental issues.