How A Rain Gauge Works

The modern rain gauge most commonly used consists of four components: an outer tube, and inner tube, a funnel and a measuring stick. The outer tube, normally 20 cm in diameter and 50 cm in height, holds the inner tube which is 1/10th the size of the outer tube. A funnel at the top of the outer tube directs water into the smaller tube. As rain falls, it is collected by the funnel and fills the smaller tube. Since the collection area is ten times the size of the storage area, measurements in the inner tube are exaggerated by a factor of ten. One inch of water in the tube equals 1/10 of an inch of rainfall. The gauge can read up to two inches of rain. Excess rain is trapped in the outer tube.