What is barometric pressure?

Many times we are getting asked about what barometric pressure is and whether pressure sensors can effectively measure it. For that reason, we have prepared this short blog article. Before jumping into the various details, let’s start with the basics.

Barometric pressure definition

The pressure within the Earth’s atmosphere is known as barometric pressure, after the instrument used for its measurement, “the barometer”.

Please note that the barometric pressure is also referred to as atmospheric pressure.

In most cases, the hydrostatic pressure caused by the air weight above the measurement point is closely approximated by the atmospheric pressure. There is less overlying air mass as elevation increases, meaning that atmospheric pressure decreases with rising elevation.

Measurement units

The standard unit of atmospheric pressure is the atmosphere (atm). One standard atmosphere, which is also referred to as one atmosphere is equivalent to:

• 1 atm = 101,325 Pa (pascal)
• 1 atm = 1,013.25 hPa (hectopascal)
• 1 atm = 1,013.25 mbar (millibar)
• 1 atm = 760 mmHg (millimeters of mercury)
• 1 atm = 29.9213 inches Hg (inches of mercury)
• 1 atm = 14.6959 psi (pound per square inch)

What is a barometer and what does it measure?

A barometer is a scientific instrument that is used in a specific environment to measure air pressure. The pattern of pressure will predict short-term changes in the weather.

In surface weather research, several measures of air pressure are used to help locate surface troughs, pressure systems and frontal boundaries. Barometers and pressure altimeters are the same instruments, but they are used for different purposes.

The altimeter is meant to be used at various heights, referring to the height of the corresponding air pressure, while the barometer is held at the same level and measures small changes in pressure caused by temperature and weather conditions.

What is a barometer used for?

In essence, by tracking the barometric pressure, one can forecast short-term weather changes.

Example 1: If the barometric pressure in an area is 1013 mbar on a given day and then it starts dropping, this means that the air is cooling, and moisture is condensing in the air. Clouds start to form, and rain is very probable.

Example 2: On the other hand, if the barometric pressure is increasing, this means that the air is warming, the skies should be clear, and the weather will be sunny.

Example 3: Extreme weather conditions can also be forecasted by correlating barometric pressure and time. That means that if it starts dropping fast, then a storm is coming!

What is considered a normal barometric pressure?

There is no standard barometric pressure as it depends on altitude.

To put it simply, if we assume that the weather conditions were the same, the standard barometric pressure at sea level would be 1013.25 mbar while at the top of Mount Everest only 300 mbar!

Barometric pressure variations due to weather have a smaller scale. In order to avoid confusion and have a common reference, barometric pressure is reported in accordance with sea-level pressure at weather reports.

Highest: With reference to sea level, the highest barometric pressure ever recorded was 1083.8 mbar at Agata, Siberia, Russia (262m altitude) on 31st December 1968.

Lowest: On the other hand, the lowest barometric pressure ever recorded was 870 mbar in a tropical cyclone on 12th October 1979 northwest of Guam, USA.

Did you know?

A failing barometer indicates that rain is very probable as the air is cooling and clouds start to form!

What sensors are used to measure it?

Many household barometers are made from liquid-filled glass tubes.

However, barometers for industrial use or for usage in weather stations are capacitive-based pressure sensors.

These sensors are extremely sensitive and accurate – up to 0.15% of full scale. A major benefit with capacitive sensors is their ability to convert a pressure reading into a digital electrical signal, a perfect solution for smart outposts that need to communicate bi-directionally with the sensor, are low power and transmit pressure information back to a central location wirelessly.