The ISO 2909:2002 standard provides two methods for calculating the viscosity index (VI) of petroleum products, respectively for products with different viscosity index ranges. Procedure A is for petroleum products with a viscosity index up to 100, while Procedure B is for products with a viscosity index of 100 and above. The standard does not apply to products with a kinematic viscosity of less than 2.0 mm ²/s at 100 ° C and provides methods for estimating kinematic viscosity at different temperatures. The viscosity characteristics of petroleum products under temperature changes can be accurately assessed through this standard, thus guiding the application and performance optimization of the product.