Atmosphere (atm)
The atmosphere, symbol atm, is a pressure unit originally based on average sea-level air pressure on Earth, defined as 101,325 pascals. First used in the 19th century for meteorology and engineering, the atmosphere is a convenient unit of measurement for expressing pressure in science, including chemistry, physics, and gas laws. Though largely replaced by SI units in formal texts, it remains widely recognized in academia and industry. Its historical role and practical magnitude sustain its relevance in global pressure measurements.
Pascal (Pa)
The pascal (Pa) is the official SI unit for pressure, defined as the force of one newton applied over an area of one square meter. This unit was named in honor of Blaise Pascal, a renowned French mathematician and physicist, and formally adopted in 1971 to harmonize pressure measurement standards around the world. The pascal is widely used in scientific, industrial, and engineering fields, particularly in disciplines like fluid dynamics and atmospheric science. Because a single pascal is a small unit of pressure, larger multiples such as the kilopascal are commonly employed for practical purposes. The introduction of the pascal helped achieve uniformity and accuracy in reporting pressure across different sectors globally.