What are the units of an altimeter?

Answered by James Kissner

The units used for altimeters can vary depending on the region. In most parts of the world, including Europe, Asia, and Australia, the common unit for altimeter calibration is hectopascals (hPa). This unit is based on the metric system and is equivalent to one millibar (mb). It is a measurement of atmospheric pressure.

However, in North America (excluding Canada) and Japan, altimeters are calibrated in inches of mercury (inHg). This unit is derived from the imperial system of measurement and is a measure of the height of a column of mercury that can be supported by atmospheric pressure.

The choice of units for altimeter calibration is largely based on historical reasons and regional preferences. It can be a source of confusion for pilots and aviation professionals who operate in different parts of the world and need to convert between the two units.

In my personal experience as a pilot, I have had to familiarize myself with both units of measurement. When flying in Europe, I am accustomed to using hectopascals, but when flying in North America, I need to convert between hectopascals and inches of mercury. This requires a quick mental calculation or referring to conversion charts and tables.

It is worth noting that altimeter settings, which are used to calibrate altimeters, are typically given in the respective units used in each region. For example, in Europe, altimeter settings are provided in hectopascals, while in North America, they are given in inches of mercury.

To ensure accurate altitude readings, pilots must regularly update their altimeter settings based on the current atmospheric pressure at their location. This is typically obtained from weather reports or air traffic control.

The units of an altimeter can vary depending on the region. Hectopascals (hPa) are commonly used worldwide, except in North America (excluding Canada) and Japan, where inches of mercury (inHg) are the preferred units. Pilots and aviation professionals operating in different regions need to be familiar with both units and be able to convert between them as necessary.