How to Convert Torr to Pascals
Converting Torr to pascals bridges a traditional pressure measurement unit with the modern SI standard. The Torr is a pressure unit named after Evangelista Torricelli, the inventor of the mercury barometer, and it is closely associated with millimeters of mercury (mmHg). It is widely used in vacuum science, thin-film deposition, and laboratory chemistry. The pascal (Pa) is the SI unit of pressure, defined as one newton per square meter, and it is the international standard for scientific and engineering pressure measurements. One Torr equals approximately 133.322 pascals. This conversion is critical for vacuum system engineers specifying pump performance, materials scientists reporting deposition conditions, chemists converting laboratory pressure measurements to SI units, and physicists expressing experimental conditions in internationally standardized terms. Accurate Torr-to-pascal conversion ensures consistency and clarity in scientific communication across disciplines and borders.
Conversion Formula
To convert Torr to pascals, multiply the pressure in Torr by 133.322. This conversion factor is derived from the definition of the Torr as exactly 1/760 of a standard atmosphere. Since 1 atm = 101,325 Pa, one Torr equals 101,325 / 760 = 133.322368... Pa, commonly rounded to 133.322. This provides a precise bridge between the traditional mercury-based pressure measurement and the modern SI framework.
Pa = Torr × 133.322
5 torr = 666.61 pascals
Step-by-Step Example
To convert 5 Torr to pascals:
1. Start with the value: 5 Torr
2. Multiply by the conversion factor: 5 × 133.322
3. Calculate: 5 × 133.322 = 666.61
4. Result: 5 Torr = 666.61 Pa
This is a low pressure typically found in rough vacuum systems, well below atmospheric pressure of 101,325 Pa.
Understanding Torr and Pascals
What is a Torr?
The Torr is named after Evangelista Torricelli (1608-1647), the Italian physicist and mathematician who invented the mercury barometer in 1643. Torricelli demonstrated that atmospheric pressure could support a column of mercury approximately 760 mm tall, laying the foundation for pressure measurement science. The unit was formally named in his honor and defined as 1/760 of a standard atmosphere. The Torr gained widespread adoption in vacuum science during the 20th century as mercury manometers were the primary instruments for measuring sub-atmospheric pressures. Although the SI system advocates for the pascal, the Torr remains deeply embedded in vacuum technology, plasma physics, thin-film science, and laboratory chemistry.
What is a Pascal?
The pascal honors Blaise Pascal (1623-1662), the French mathematician and physicist renowned for his contributions to fluid mechanics and pressure theory. Pascal conducted landmark experiments proving that atmospheric pressure decreases with altitude and formulated Pascal's law of pressure transmission in fluids. The unit bearing his name was adopted as the SI unit of pressure in 1971, defined as one newton per square meter. The pascal provides a coherent unit within the SI system, directly linking pressure to the fundamental units of force and area. Although the pascal is very small for many practical applications (atmospheric pressure is about 101,325 Pa), its multiples are widely used: kilopascals for tire and blood pressure, megapascals for material strength, and gigapascals for geological pressures.
Practical Applications
Vacuum system manufacturers specify pump base pressures in Torr and convert to pascals for international product documentation. Semiconductor fabrication facilities measure process chamber pressures in Torr but report to international quality standards in pascals. Thin-film deposition researchers specify sputtering and evaporation pressures in Torr for legacy equipment while publishing in pascals for modern journals. Freeze-drying (lyophilization) equipment used in pharmaceutical manufacturing often displays pressure in Torr, requiring conversion to pascals for regulatory filings. Mass spectrometer operators working in the milliTorr range convert to pascals for instrument comparison and specification sheets.
Tips and Common Mistakes
A common mistake is confusing Torr with mmHg. While they are nearly identical for practical purposes (the difference is less than 0.000015%), they have distinct formal definitions. The Torr is defined as exactly 1/760 atm, while mmHg depends on the physical properties of mercury under specified conditions. Another error is using 133.3 instead of the more precise 133.322, which can matter when dealing with very low pressures in vacuum science where small differences are significant. When working in the milliTorr or microTorr range, be particularly careful with unit prefixes: 1 mTorr = 0.133322 Pa. Always double-check whether a source is using Torr or milliTorr, as a factor-of-1000 error can ruin an experiment.
Frequently Asked Questions
One Torr is defined as exactly 1/760 of a standard atmosphere, which equals 101,325/760 = 133.32236842... Pa. The commonly used value of 133.322 Pa per Torr is rounded to six significant figures. For most scientific applications, this precision is more than adequate. The exact value is an irrational repeating decimal because 760 does not divide evenly into 101,325.