Measuring Precipitation

Precipitation is the name given to the various ways in which water falls from the sky and reaches the ground. This can include drizzle, rain, sleet, hail and snow.

The amount of rainfall can be important for a variety of reasons. People who grow plants like to know how much rain has fallen. Those who live near rivers may be affected by how much rain there has been.

This page is just an introduction to Precipitation. To see more you can go to More About Precipitation. Here there is an example of a digital rain gauge.

When you have finished reading about this you may want to return to Collecting Data.

Units of Measurement

Rain is measured in millimetres. This is because you are measuring the depth of the rain which has fallen.
The scale on this gauge goes up in ones, with a number on every fifth line. You need to count on or back from the nearest number.
It is not measured in millilitres. We are not trying to measure the total amount of rain which has fallen.

The Rain Gauge Scale

A funnel shape is used so that when there is only a little rain it is easier to measure. You can see that the markings at the bottom are further apart because the funnel is narrower there. Nearer the top, where the funnel is wider, the markings are closer together. Record ½ as ·5, ¼ as ·25 and ¾ as ·75.

Keeping it Level

When measuring the rain you need to keep the gauge very level. Take the funnel off its spike and place it on a flat surface. Look at the picture to see the weather watcher reading the scale carefully.

How not to do it!

Tipping the gauge on its side will give an incorrect reading. This is true in most capacity procedures. The two images on the right show the same amount of water. See how the reading changes if it is not level.


When the temperature is cold, precipitation will take the form of snow. It is usual to measure its depth in millimetres. Do make sure that your ruler does not have a 'dead end' or extra bit on the end which is not included in the measurement. A metal ruler like the one in the picture is a good one to use. Clear the area where you measured the snow. You want a fresh start in case you need a reading the next day!

Hail and Sleet

There is rarely an opportunity to observe this at the time of taking the weather readings. It is usually treated as any other precipitation, as it melts into the rain gauge.
Hail is rain which has frozen. It can be seen to bounce of the ground.

In Great Britain the term sleet is used to describe a mixture of rain (or drizzle) and melting snow.