A rain gauge is used to measure how much rain or melted snow has fallen. Rainfall is reported in inches or centimeters. It is a barrel shaped container with a funnel on top. On the side are inch or centimeter markings. Each day after it rains you look to see how much rain has fallen. Rainfall amount tells us if we might have a flood. Farmers need to know in case there isn't enough rainfall then they'll have to water their crops.