A cup of plain, uncooked rice contains anywhere from 5,000 to 10,000 grains. The number of grains found in a cup of rice varies considerably by the variety of rice, as there are over 40,000 types of rice throughout the world, each of varying shape and size. Plain, uncooked rice is most often used in math experiments among school students and experiments.
More grains of short-grain rice than long-grain rice are contained in a cup. Rice expands to three times its original size after cooking. A cup of cooked rice contains about a third of the number of grains found in a cup of uncooked rice.