The TAPPI T 261 standard specifies a method for the measurement of the weight fraction of fine powder in pulp by a wet sieve method. This method separates and weighs the fine powder in a pulp sample through a single-layer sieve classifier to calculate the percentage of fine powder to the total weight. This method can also be used to evaluate the fiber retention tendency of fine powder under different turbulent conditions. The standard is suitable for the paper industry to help optimize pulp mass and control the fine powder content in the production process, thereby improving paper performance and product mass.