A viscosity classification for industrial liquid lubricants established by ISO 3448 and based on kinematic viscosity at 40°C. The grade number, such as ISO VG 46, identifies a viscosity range centred approximately on that number in square millimetres per second; it does not specify lubricant quality or application performance. ISO 3104 is a test method used to determine kinematic viscosity, not the viscosity-grade standard.
