# What are the weather units of measurement and which ones are best to use

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In meteorology, the data is collected by special weather instruments and measured using a set of special weather units. Some of these you already know well: for example, degrees for temperature. But there are others for many other weather elements.

In this article, we'll understand where the weather units of measurement come from, what alternatives they have, and which ones are best to use for your region and outdoor activity. You will also learn how to change and convert them if necessary.

## What are the weather measurement units?

Weather measurement units are special units adopted to measure and denote various weather elements. Like other non-weather unites, they come from the International System of Units (SI), a modern version of the metric system now accepted in most countries of the world.

For weather, we are primarily talking about the three main weather elements: air temperature, precipitation (rain and snow), and wind. They are measured in degrees Celsius (°C), millimeters (mm), and meters per second (m/s), respectively. These are the units of measurement of weather according to the International SI. Other unites are used for other weather elements.

The essence of the system is that it assigns only one unit to one element — as in the above cases — and recommend using it as the main unit to avoid confusion over using different units in different parts of the world, as was the case before. This has already been achieved. Today the system is used all over the world only except the United States and a few other small countries, many of which, however, are also planning to switch to the metric system.

## How to use weather units of measurement?

The World Meteorological Organization (WMO) states that “the SI should be used as the system of units for the evaluation of meteorological elements included in reports for international exchange". In particular, the following units for the weather elements are recommended by the WMO for meteorological observations.

But before we give the list, it is important to note that some of them are basic elements — you can find them in any weather forecast, some are advanced — they are available in specialized weather forecast, and figuratively speaking, the “very” advanced ones — are only used by professional meteorologists, in normal life you are unlikely to ever see them.

Anyway, the elements recommended by WMO are the first in the list below. But we also give other units that are used for this or that parameter in the United States and some other countries that you may also encounter and use:

• Air temperature: degrees Celsius (°C) or Kelvins (K). Other units: Fahrenheit (ºF).
• Precipitation (total amount): millimeters (mm) or kilograms per square meter (kg/sq m). Other units: inches (in).
• Wind speed: meters per second (m/s). Other units: miles per hour (mph), kilometers per hour (kph), knots (knt = 0.514 m/s, 1.15078 mph, 1.852 kph, 1 nautical mile per hour), beaufort (Beaufort wind force scale).
• Wind direction: degrees clockwise from north or on the scale 0-36(0), where 36(0) is the wind from the north and 9(0) is the wind from the east (°). Other units: cardinal directions (north (N), south (S), west (W), east (E) and others).
• Atmospheric pressure: hectopascals (hPa). Other units: millimeter of mercury (mmHg), inches of mercury (inHg).
• Relative humidity: per cent (%).
• Visibility: meters (m). Other units: kilometers (km), feet (ft).
• Sunshine duration: hours (h). Other units: minutes (min), seconds (s).
• Cloud height: metres (m). Other units: feet (ft).
• Cloud cover (amount): oktas. Other units: per cent (%).
• Precipitation intensity (Ri): millimetres per hour (mm/h) or kilograms per m-2 per second (kg/sq m/s).
• Snow water equivalent: kilograms per square meter (kg/sq m).
• Evaporation: millimetres (mm).
• Irradiance: watts per square meter and radiant exposure in joules per square meter (W/sq m, J/sq m).
• Geopotential, used in upper-air observations: standard geopotential metres (m′). Note: height, level or altitude are presented with respect to a well-defined reference. Typical references are Mean Sea Level (MSL), station altitude or the 1013.2 hPa plane.

The main weather units of measurement according to the World Meteorological Organization (WMO. Valerya Milovanova / Windy.app

Well, this is how the weather is measured. Now you have a list of basic and advanced units recommended by WMO.

However, it is far from complete. There are many more of both types: weather conditions, feels like temperature, wind gusts, Ultraviolet Index, snow depth, and others. To find out what these elements are, check out "The list of weather elements and data used in the Windy.app".

So the answer to the question “Which units are best to use”, which is put in the title of the article, will be the following: the ones that are more comfortable for you. And there are many such cases.

For example, the WMO recommends using meters in seconds (m/s) to measure speed, but knots (knt) or nautical miles are very common in sailing and aviation instead of the usual miles or meters and kilometers. Or another example: for clouds, the okta is traditionally used, but to an ordinary user today this symbol does not say much about anything, it is much clearer to him/her than to see usual percentages (of the coverage of the sky by clouds). And so on...

However, if you are interested in meteorology and want to be an expert in weather forecasting, knowing all the existing units is very desirable, if not obligatory.

## Where to get weather measurement units?

In Windy.app, you will find more than 100 different weather elements in different units of measurement throughout the app: on the Home Screen, Weather Map, Spot Screen, and Weather Stations.

The units are set by default based on your region, that is, the two parts of the world: the United States and the rest of the world. But you can change them at your discretion if you are used to one or the other. To do this, go to the appropriate Unit section of the Main menu of the app from the Home screen or from the Weather Profiles selection page on the spot.

Read more about how to do this in a separate tip in the Support section.

Weather units of measurement in the Windy.app for iOS

Weather measurement units in the Windy.app for iOS

Text: Ivan Kuznetsov, an outdoor journalist, editor and writer from the Dolomites, Italy, and Karelia, Finland, with 10 years of professional experience. His favorite sports are hiking, cycling and sauna. Read his other articles

Cover photo: Martin Wyall / Unsplash

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