The grain size of soil particles are categorized into three groups: clay, silt, and sand. Clay measures less than 0.002 mm (0.0008 inch) in diameter, silt is between 0.002 mm (0.0008 inch) and 0.05 mm (0.002 inch), and sand is between 0.05 mm (0.002 inch) and 2 mm (0.08 inch).