Assuming you are talking about white rice, 1/2 cup of raw rice will make approximately 1 cup of cooked rice. This is based on cooking the rice in 2 cups of water, which is the standard ratio for cooking white rice.
If you are using a different type of rice, the cooking time may be different and you may need to adjust the amount of water you use. For example, basmati or jasmine rice only need 1 1/2 cups of water for every 1 cup of dry rice.