Rainfall is now being measured in most parts of the world by means of an instrument called a rain gauge. The gauge of the United States Weather Bureau is shaped like a hollow tube closed at the lower end, with a funnel in the top.

This gauge is placed in an unsheltered place, and a graduated scale shows exactly how much rain has fallen in it. The Weather Bureau says that there has been an inch of rainfall if enough rain has fallen to make a sheet of water an inch deep over a given area.