A rain gauge is a type of instrument used by meteorologists to gather and measure the amount of falling precipitation, rain.

Most rain gauges generally measure the precipitation in millimeters. The level of rainfall is sometimes reported as inches or centimeters.

Types of rain gauges include graduated cylinders, weighing gauges, tipping bucket gauge, and simple buried pit collectors. Each type has it advantages and disadvantages for collecting rain data.

Rain gauges have their limitations. Attempting to collect rain data in a hurricane can be nearly impossible and unreliable (even if the equipment survives) due to wind extremes. Also, rain gauges only indicate rainfall in a localized area. An extreme example of this is the annual rainfall in Seattle: the official weather station for the city is at Seattle-Tacoma International Airport, the driest part of the city, and the gauge itself was placed, by chance, at the driest part of the airport. Actual annual rainfall for the city is around ten inches greater than the official records indicate.

See also: disdrometer, millimeter