One way to guess how many jelly beans is to count the number of jelly beans to get the length and width of the jar, if it is square. Then multiply those figures together to get about how many jelly beans are in a layer. Then multiply by the number of layers in the jar. Take about 75 to 85 percent of your answer as your estimate, because the jelly beans won't be perfectly packed. If your jar is round, you can't multiply by height and width directly, but you can use your answer as a rough, high estimate.