The planting depth of rice grain is about 2-4 cm. This means that when planting rice, the seeds should be buried in the soil at a depth of 2-4 cm. This is the recommended depth for optimum growth and development of rice plants. Planting at a depth that is too shallow or too deep can lead to poor germination and low yield. Therefore, it is important to ensure that the planting depth is appropriate when planting rice.