What is Barometric Pressure and How Can You Measure It?

Barometric pressure, also known as atmospheric pressure, plays a crucial role in weather forecasting, aviation, environmental science, and outdoor activities. Understanding what it is, how it works, and how to measure it can provide valuable insights into changing weather patterns, altitude variations, and broader climate conditions.

What is Barometric Pressure?

Barometric pressure is the force exerted by the weight of the atmosphere above a specific point. At sea level, this pressure averages about 1013.25 millibars (mb) or 29.92 inches of mercury (inHg), though it fluctuates depending on weather systems and altitude.

Air is composed of molecules that have mass. The cumulative weight of these molecules pressing down on Earth creates barometric pressure. It decreases with elevation because the density of air—and consequently the number of air molecules—decreases as you go higher.

Barometric pressure is fundamental to understanding weather because it reflects the behavior of air masses. High-pressure systems are usually associated with clear, calm weather, while low-pressure systems often bring clouds, wind, and precipitation.

Want to understand how barometric pressure differs from station pressure? Read our in-depth explanation here.

Why Barometric Pressure Matters

Changes in barometric pressure are indicative of shifts in weather. For example:

• Falling pressure often signals that a storm or low-pressure system is approaching.
• Rising pressure typically indicates improving weather conditions associated with high-pressure systems.

These fluctuations are vital for:

• Weather forecasting: Meteorologists monitor pressure trends to predict weather changes.
• Aviation: Pilots rely on accurate pressure readings to determine altitude and ensure safe navigation.
• Outdoor safety: Hikers, mountaineers, and hunters monitor barometric pressure to anticipate sudden weather changes.
• Scientific research: Environmental scientists use barometric data to study atmospheric conditions and their impact on ecosystems.

Units of Measurement

Barometric pressure is measured in several different units, depending on regional and scientific standards:

• Millibars (mb): Commonly used in meteorology, especially in the United States.
• Inches of mercury (inHg): Often used in aviation and weather forecasts.
• Hectopascals (hPa): Preferred in most international weather services. 1 hPa = 1 mb.
• Pascals (Pa): The SI (International System of Units) standard, used in scientific contexts.

Instruments for Measuring Barometric Pressure

Measuring barometric pressure accurately requires specialized tools known as barometers. These instruments come in various types, each suited to specific needs and environments.

Mercury Barometers

Invented by Evangelista Torricelli in 1643, the mercury barometer is the oldest and most well-known type. It consists of a glass tube filled with mercury, inverted in a basin of mercury. The height of the mercury column changes with atmospheric pressure:

• Higher pressure forces more mercury up the tube.
• Lower pressure results in a shorter mercury column.

Advantages:

• High accuracy
• Long-standing reliability

Disadvantages:

• Fragile and bulky
• Contains toxic mercury
• Sensitive to temperature

Aneroid Barometers

An aneroid barometer uses a sealed, flexible metal chamber (aneroid cell) that expands and contracts with changes in air pressure. These mechanical changes move a needle on a dial, giving a pressure reading.

Advantages:

• Mercury-free and more portable
• Durable and widely used in field instruments and altimeters

Disadvantages:

• Requires occasional calibration
• Less precise than mercury in laboratory settings

Digital Barometers: The Smartest, Most Convenient Choice

Digital barometers are the modern standard for fast, accurate, and easy-to-read atmospheric pressure data. Unlike traditional mercury or aneroid barometers, digital models don't require calibration, maintenance, or delicate handling. Instead, they use advanced pressure sensors and microprocessors to deliver real-time, reliable data—often alongside temperature, humidity, altitude, and even wind readings.

These highly portable devices are compact, intuitive, and often packed with features like data logging, trend tracking, and wireless connectivity, making them ideal for both professional and recreational use in the field or on the job.

Why Choose a Digital Barometer?

• Instant, accurate pressure readings
• Built-in environmental sensors (temperature, humidity, altitude)
• Compact and rugged - no fragile glass or moving parts
• Wireless data sync options and onboard data logging
• Trusted across industries: weather monitoring, construction, firefighting, hiking, aviation, and more

Kestrel® digital weather meters with barometric pressure sensors include:

• Kestrel 2000 - An affordable, entry-level weather meter with pressure-based altitude
• Kestrel DROP D3 - Rugged data loggers that track pressure over time and sync via Bluetooth
• Kestrel 5500 - A full-featured environmental meter with barometric pressure, wind, heat stress index, and more

How to Measure Barometric Pressure

Understanding how to measure barometric pressure accurately is essential for interpreting weather trends, estimating altitude, and enhancing safety in outdoor and technical activities. Choosing the correct tool and following best practices ensures precise and meaningful readings.

1. Choose the Right Barometer

Select a barometer based on your application:

• For field use or portable applications, digital or aneroid barometers are ideal.
• For stationary, high-precision measurements, mercury barometers are sometimes still used in controlled lab environments.


2. Calibrate Your Device

Ensure the device is correctly calibrated to the local sea level pressure. Since pressure decreases with altitude, failing to adjust for elevation can skew results.

3. Take the Reading

Place the barometer in a location with stable temperature and minimal airflow. Read the pressure value in your preferred unit.

• With analog models, note the needle position.
• With digital models, the value will display on the screen.


4. Monitor Trends

One-time readings provide a snapshot, but trends tell a deeper story. Record barometric pressure regularly to observe changes and predict short-term weather shifts.

Measuring Altitude with Barometric Pressure

Barometric pressure is inversely related to altitude. The higher you go, the lower the pressure. This relationship allows pressure to be used to estimate altitude, a principle used in altimeters.

Applications include:

• Aviation: Aircraft altimeters rely on pressure to determine altitude.
• Mountaineering and hiking: Handheld altimeters or smartwatches use barometric pressure to estimate elevation.
• Skydiving: Pressure-based altimeters help monitor free-fall altitude.

However, changing weather can affect barometric readings, so recalibration may be needed to maintain accuracy.

The Role of Barometric Pressure in Weather Forecasting

Weather systems are driven by differences in air pressure. Meteorologists use barometric readings to:

• Map pressure systems using isobars on weather charts
• Predict wind directions and speeds
• Forecast weather changes with rising or falling pressure trends

For example:

• High pressure = sinking air, drier weather, light winds
• Low pressure = rising air, cloud formation, precipitation, and storms

Rapid drops in barometric pressure are often a sign that severe weather is imminent.

Where to Access Barometric Pressure Data

If you don't have a barometer, you can access local barometric pressure readings from various sources:

• Weather apps and websites: Most platforms provide current pressure readings.
• Airport METAR reports: Pilots rely on these reports for pressure and weather conditions.
• Local news and weather broadcasts: These often include barometric pressure as part of the forecast.
• Environmental monitoring stations: Government and research facilities often publish live sensor data.

Choosing a Barometric Pressure Device

When selecting a barometer, consider:

• Accuracy: Higher-end devices provide more precise readings.
• Durability: Essential for outdoor or rugged applications.
• Ease of Use: Digital models offer simplicity and integration.
• Functionality: Multi-sensor units give added value for outdoor, scientific, or technical use.

Brands like Kestrel Instruments, for example, offer reliable and compact weather meters that include barometric pressure sensors, making them popular among professionals in meteorology, firefighting, aviation, and field research.

Putting Barometric Pressure to Work

Barometric pressure is more than just a number on a weather forecast—it's a powerful indicator of environmental change. By understanding what barometric pressure is and how to measure it, individuals and professionals alike can better prepare for changing weather, navigate terrain safely, and optimize performance in a wide range of applications. Whether you're a hiker, a pilot, a scientist, or simply someone who enjoys watching the weather, keeping an eye on barometric pressure helps you stay informed and aware of your environment.