Altimeter and Barometer The Difference Between Them

Altimeter and Barometer are two important instruments used in aviation and meteorology. Both instruments measure atmospheric pressure but in different ways. The difference between these two instruments lies in their application and usage. In this article, we will explore the differences between Altimeter and Barometer in detail.


A barometer is an instrument used to measure atmospheric pressure. It was invented by Evangelista Torricelli in 1643. A barometer consists of a glass tube filled with mercury or other liquid metal. The tube is closed at one end and open at the other end. The open end of the tube is placed in a dish of mercury. When the pressure outside the tube changes, the level of mercury inside the tube changes accordingly. The height of the mercury column is directly proportional to the atmospheric pressure. A standard atmospheric pressure of 1013.25 hPa (hectopascals) is equal to a column of mercury of 760 mm in height. This is also known as 1 atmosphere or 1 bar.

There are two types of barometers: mercury barometer and aneroid barometer. Mercury barometers are the most accurate and reliable. They are used as standard instruments for measuring atmospheric pressure. Aneroid barometers are smaller and more portable. They use a small metal capsule that expands or contracts with changes in atmospheric pressure. The movement of the capsule is amplified by a system of levers and springs and displayed on a dial.


An altimeter is an instrument used to measure altitude or height above sea level. It is an essential instrument in aviation. It allows pilots to determine their height above the ground and to maintain a safe altitude during flight. Altimeters are also used in mountaineering and hiking to measure altitude.

An altimeter works by measuring atmospheric pressure. As altitude increases, atmospheric pressure decreases. An altimeter measures this decrease in pressure and converts it into a height reading. The altimeter consists of an aneroid capsule that expands or contracts with changes in atmospheric pressure. The capsule is connected to a set of gears and a pointer. As the capsule expands or contracts, the pointer moves to indicate the altitude.

There are two types of altimeters: barometric altimeter and radio altimeter. Barometric altimeters use atmospheric pressure to measure altitude. They are the most common type of altimeter used in aviation. Radio altimeters use radio waves to measure altitude. They are used in low altitude situations such as takeoff and landing.

Differences between Altimeter and Barometer:

  1. Purpose:

The main difference between Altimeter and Barometer is their purpose. A barometer is used to measure atmospheric pressure, while an altimeter is used to measure altitude.

  1. Units of measurement:

Barometers measure atmospheric pressure in units such as hPa or inches of mercury. Altimeters measure altitude in feet or meters.

  1. Calibration:

Barometers and altimeters need to be calibrated regularly to ensure accurate measurements. Barometers are calibrated using a known weight, while altimeters are calibrated using a known altitude.

  1. Sensitivity:

Barometers are more sensitive than altimeters. They can detect even small changes in atmospheric pressure. Altimeters are less sensitive since they are designed to measure changes in pressure due to changes in altitude.

  1. Range:

Barometers have a wider range of measurement than altimeters. They can measure atmospheric pressure at any altitude, while altimeters are limited to measuring altitude within a certain range.

  1. Usage:

Barometers are used in meteorology and weather forecasting to measure atmospheric pressure. Altimeters are used in aviation to measure altitude.

  1. Accuracy:

Barometers are more accurate than altimeters. They are used as standard instruments for measuring atmospheric pressure. Altimeters have an accuracy of about 100 feet and are subject to errors due to changes in temperature, humidity, and barometric pressure.

  1. Type of instrument:

Barometers are typically either mercury or aneroid barometers. Aneroid barometers are smaller and more portable than mercury barometers. Altimeters are typically barometric altimeters or radio altimeters. Barometric altimeters are more common in aviation and are required to be installed in all aircraft.

  1. Operating principle:

Barometers operate on the principle that atmospheric pressure changes with altitude. Altimeters operate on the same principle but are calibrated to measure altitude directly.

  1. Applications:

Barometers are used in meteorology, weather forecasting, and research. They can also be used for measuring altitude in non-aviation applications. Altimeters are primarily used in aviation but can also be used in mountaineering, hiking, and other outdoor activities.


In summary, Altimeter and Barometer are both instruments that measure atmospheric pressure but for different purposes. Barometers measure atmospheric pressure and are used in meteorology, weather forecasting, and research. Altimeters measure altitude and are primarily used in aviation. While both instruments operate on the same principle of changes in atmospheric pressure, they differ in their calibration, sensitivity, range, and accuracy. It is important to understand the differences between these instruments to ensure accurate measurements and safe operation in aviation and other applications.