When meteorologists report that 30 mm of rain has fallen, it always seems like more. How is rain measured?
measured with two types of gauges, both having different surface areas. One has a surface area the size of a coffee tin or around a 30 square centimetre opening. This is the worldwide standard rain gauge. The other type is a little larger with a 120 square centimetre opening, and it’s called a tipping rain gauge. 30 mm of rain on these types of rain gauges does not sound as impressive as over a larger area, for example, a square kilometre with 30 mm of rain equals many thousands of tonnes of water.
