torr

Torr is a unit of pressure named after the 17th-century Italian physicist Evangelista Torricelli. It is defined as one standard atmosphere divided by 760, making 1 Torr exactly 133.322368427 pascals. By convention, 1 Torr is equivalent to 1 millimeter of mercury (mmHg), and thus 1 atm equals 760 Torr. The torr is used in many scientific and engineering contexts, particularly in vacuum technology, as an alternative to pascals or atmospheres.

Historically, the torr arose from early barometry and vacuum studies. Torricelli’s development of the mercury barometer linked atmospheric pressure to a measurable height of mercury, which later led to the adoption of the torr as a practical pressure unit. In modern practice, pressure can be expressed in pascals, atmospheres, torr, or mmHg, depending on field, region, and instrument conventions.

In practical use, torr remains common in vacuum science and related disciplines. Vacuum gauges such as Pirani, thermocouple, and ionization gauges often report readings in Torr or in related units. Typical ranges span from atmospheric pressure (about 760 Torr) to high and ultra-high vacuum regions well below 1 Torr, sometimes reaching 10^-9 to 10^-12 Torr in specialized equipment.

Beyond the unit, Torr is also used as a surname and may appear in place names. The primary significance of the term in scientific contexts is the pressure unit, standardized and widely recognized in research and industry.