Rainfall is extremely variable, both over time and between different locations, which makes it very difficult to measure. A rain gauge basically collects water falling on it and records the change over time in the rainfall depth, which is usually expressed in mm.

## What does mm of rainfall means?

Meteorologists measure rain volume received in a unit of time. So 1 mm of rain translates to 1 litre of water in a single metre square. So 802 mm of rain would mean that a single metre square would receive 802 litres of rain, 140 mm would mean 140 litres of water received in a single metre square, and so on.

## Why rainfall is measured in depth?

The total amount of rainfall over a given period is expressed as the depth of water which would cover a horizontal area if there is no runoff, infiltration and evaporation. The catch of rainfall is a function of the height of the gauge; the more open the location the greater will be the difference in catch with height.

## How do you calculate rainfall in mm?

Heres what youll need to do:Measure the diameter of the bucket at the level of the rain. Measure the diameter of the bucket at the bottom in the same way.Calculate the average of the two diameters.Divide by two to find the average radius.Find the average volume of rain = Depth x radius x radius x 3.14. •Sep 16, 2013