Bar UnitEdit
The bar is a unit of pressure used in many scientific, engineering, and industrial contexts. Defined as exactly 100,000 pascals, it provides a convenient decimal-based alternative to the atmosphere for describing everyday and technical pressure levels. The bar is not an SI base unit, but it is widely recognized and employed, especially in meteorology, automotive engineering, and various fields of physics and engineering. When written, the symbol is typically lower-case bar, and in formal terms the bar can be viewed as a non-SI metric unit aligned with the broader system of units in use around the world. Bar (unit) is the common display for this measurement, with the value sometimes given in relation to other pressure scales such as the Pascal or the Atmosphere (unit).
Bar origins and standardization The bar emerged in the early 20th century as practitioners sought a decimal-based unit of pressure close to typical atmospheric levels. Over time, the bar gained traction across European engineering communities and spread into meteorology, oceanography, and industry. It is now widely used in many parts of the world, particularly where engineers and technicians prefer a straightforward, readable unit for pressure readings. The bar is recognized and defined in relation to the SI system as 100,000 pascals, making it easy to convert to and from the SI unit. Related concepts and standards are discussed within the broader framework of ISO 80000 and other standardization efforts overseen by organizations such as the International Organization for Standardization and historical bodies like the CGPM.
Definition, conversions, and practical use - Definition: 1 bar = 100,000 Pa = 10^5 N/m^2. This exact value means that the bar represents a precise amount of pressure in the SI framework, even though the bar itself is not an SI unit. For reference, 1 bar is about 0.986923 atmospheres, and 1 bar is approximately 14.5038 pounds per square inch (psi). Pascal is the SI unit from which the bar is derived in numerical terms, and the relationship to Atmosphere (unit) is often useful in practical contexts. - Common usage: The bar is widely seen in tire-pressure labeling, industrial specifications, and scientific reports where a compact, decimal-friendly scale improves readability. In tire maintenance and vehicle manuals, for example, pressures are frequently given in bars, with the corresponding values easily translated to psi or atm if needed. Tire pressure discussions commonly reference bar values. - Submultiples and related units: Subdivisions such as the Millibar (1 mbar = 100 Pa) and the decibar (0.1 bar) are used in specialized contexts, particularly in meteorology and oceanography. In high-pressure physics and geology, larger units like the Kilobar (1000 bar) are employed for describing intense pressures encountered in deep-earth studies and laboratory experiments. Decibar, Kilobar, and Millibar are standard terms linked to the bar in both technical literature and standard references.
Usage across disciplines - Meteorology and oceanography: The bar and its decibar and millibar relatives are convenient for reporting atmospheric and ocean pressure data, where a decimal-based system aligns with other meteorological measurements. Barometer readings are often reported in bars or millibars, depending on historical convention and regional practice. Barometer and Pressure are central concepts in this field. - Automotive and mechanical engineering: In the automotive industry, tire specifications, hydraulic systems, and many mechanical tolerances routinely use bar as a practical unit of pressure, blending familiarity with precision. - Industrial and scientific research: In physics and engineering laboratories, the bar is used for descriptions of gas pressures, vacuum levels, and process controls, complementing the SI base unit framework with a familiar, human-readable scale.
Controversies and debates As with any non-SI unit that remains widely used, debates center on standardization and clarity. Proponents of strict SI compliance argue that measurements should ultimately be expressed in pascals to avoid mixing unit systems and to ensure consistency across disciplines and international borders. Critics of over-precision in contexts where the bar’s decimal nature provides readability point to potential confusion when collaborating with teams trained primarily in atmospheres or psi. In practice, both systems persist because each offers advantages in particular domains, and conversion between them is straightforward for practitioners who understand the relationships between bars, pascals, atmospheres, and psi. The ongoing conversation in standardization bodies emphasizes clear definitions, unambiguous notation, and robust guidance for multilingual and international scientific communication.
See also - Pressure - Bar (unit) - Pascal - Atmosphere (unit) - Millibar - Decibar - Kilobar - Barometer - Tire pressure - ISO 80000