How to Measure Rainfall in Millimetres and Inches Using a WMO Standard Rain Gauge.

Rainfall is a natural phenomenon and it has its own importance and significance. Weather stations and observatories measure rainfall worldwide. The most commonly used method is the manual standard rain gauge. Rain gauges are usually very simple to use and are very accurate. There are many different types of rain gauges available on the market. Some of them are very expensive while some of them are very cheap. Here we are going to explain how to measure rainfall in mm and inches using a standard world meteorological organization (WMO) approved manual rain gauge.

The measurement of rainfall is a very important part of weather forecasting. The amount of rainfall per unit area is called “rainfall” or “precipitation.” Rainfall is a direct measure of the amount of water falling from the sky.

1. What is a Rain Gauge?

Rain gauges are simple devices used to measure the amount of rain that falls on a surface. They are usually made from a plastic or metal box with an opening at the top. A hole is drilled in the bottom of the funnel, through which water flows into a container.. The water level in the container rises as the rain falls. The rain gauge can be set up in a number of ways. It can be placed on a window sill, outside, on the ground, etc. The most important thing to remember when setting up a rain gauge is to make sure that it is positioned in a way that allows water to flow freely from the sky into the container.

There are many different types of rain gauges available on the market. Some are large and bulky while others are small and portable. The one you choose should depend on what you plan to do with the data you collect. You can use a rain gauge to measure rainfall in a specific area or you can use it to collect rainfall data for a longer period of time.

2. How to Measure Rainfall Using Rain Guage:

Rain gauges are used to measure the amount of rainfall that has fallen in a specific time period. These devices consist of a container that stores rainwater. A measuring Cylinder is used to record the amount of rainfall that has fallen in a specific time period.

To measure rainfall using a standard rain gauge as per WMO standards remove the funnel and open the lid of the rain gauge. Pour rainwater stored in the rain gauge into a standard measuring cylinder. The standard measuring cylinder is labeled in mm. Read the value in mm.

3. Rain Gauge Components:

Standard rain gauges used at weather observatories contain the following parts:


Water pours down into the container through the funnel. The funnel is made of metal or plastic. The metal funnel is more durable than the plastic one. Make sure that the funnel is well-made. If you have a metal funnel, it is a good idea to clean it regularly. If you have a plastic funnel, you can simply rinse it with water and let it dry. The funnel should also be fitted properly. It should fit snugly into the container.


Rainwater is collected in the container. The container is the part of the rain gauge that contains the water. Make sure that the container is well-made. If it is poorly made, the water will leak out of the container.WMO standard rain gauges are made up of metal.

Outer Body

The outer part of the rain gauge encloses the funnel and container.

Standard  measuring cylinder

Rainwater deposited in the rain gauge is measured in a standard cylinder labeled in mm. When we collect rainwater, we need to know how much water we have collected. The number that is given is called the rain gauge reading. For example, if we have collected 10 milliliters of water in a rain gauge, the rain gauge reading would be 10ml.

4. How to Operate a Rain Gauge

Rain gauges are useful devices that help us to observe the amount of rainfall. The best way to understand rain gauges is to learn how to operate them. If you look at a rain gauge, you’ll see that it has four parts. The first part is the funnel. This part is used to direct the rainwater into the second part of the rain gauge. The second part is the container. It is here that the rainwater is collected. The third part is the standard measuring cylinder. Here, the rainwater is measured in millimeters. You should empty the rainwater from the container into the measuring cylinder. Then, read the amount of rainfall from the millimeter label on the measuring cylinder. The fourth part is the outer enclosure of rain gauge which holds the container and funnel inside it.

5. Calculating Rainfall in mm and Inches Using Rain Gauge:

As stated earlier how measure rainfall in mm using a standard rain gauge and a cylinder, now we will discuss how to measure rainfall in inches. To measure rainfall in inches convert mm into inches.

1 inch =25.4 mm

1mm=1/25.4 inches=0.0393701inches.

At WMO-approved weather stations, each station sends weather data including the rainfall data in weather SYNOP at standard SYNOPTIC hours.

Final Thoughts:

Rain gauges come in different sizes and shapes. For example, you can choose from a small, handheld, digital rain gauge; a larger, fixed unit; a heavy-duty, stationary gauge; and a portable rain gauge. There are a variety of gauges that are ideal for a variety of uses. It is important to know about a rain gauge before you buy one. If you are using a digital rain gauge, you will need to calibrate it. This is a simple procedure that is usually explained in the product installation guide. You will need to download calibration software to make sure that the readings collected are accurate. You can also adjust the sensitivity of the gauge.

Rain gauges are available in the marketplace at various prices. For a large-sized rain gauge, the price might range from $100 to $300. But if you purchase a smaller gauge, it could cost as little as $10. However, if you need a specific rain gauge for your property, you should get the best deal possible. When buying a rain gauge, there are many factors that you will want to consider. You will need to decide on the size, shape, and style of your rain gauge.

If you are using an analog gauge, make sure that the unit is not broken or missing any parts. Also, ensure that the rain gauge is calibrated regularly.

Holds BS Degree in Electrical Engineering and MS Degree in Meteorology and currently working in the field of meteorology as an assistant weather forecaster. Love helping people know what the weather is doing. Researcher of the weather conditions and make forecasts for several different locations.

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