Torr (torr)

A unit of pressure equal to 1/760 of a standard atmosphere (about 133.322 Pa), numerically almost identical to one mmHg. Named after 17th-century physicist Evangelista Torricelli, who invented the mercury barometer. Torr is the primary unit in vacuum technology: semiconductor chamber pressure, mass spectrometry, cryogenic systems, and space environment testing. A "rough vacuum" is ~1 torr, high vacuum is 10⁻⁶ torr, ultrahigh vacuum is 10⁻⁹ torr or lower.

The Torr (torr) is a unit of pressure with a history connected to the study of fluids, gases, and atmospheric phenomena. Evangelista Torricelli's invention of the barometer in 1643 was a landmark in pressure measurement, and subsequent work by Blaise Pascal established the mathematical foundations. The pascal — the SI unit — was named in Pascal's honor when the SI system was formalized. The Torr reflects either the SI tradition or the practical conventions of specific industries that standardized their measurements independently.

Accurate pressure measurement is critical in engineering, science, commerce, and everyday life. Using the correct unit and applying conversions precisely prevents errors that can be costly or dangerous in professional applications. MegaCalc provides instant, precise conversions for the Torr and all related units so you can work confidently across unit systems.

Conversion Table

Unit	Symbol	1 torr =
Pascal	Pa	133.322 Pa
Kilopascal	kPa	0.133322 kPa
Bar	bar	0.00133322 bar
Atmosphere	atm	0.00131579 atm
Pound per Square Inch	psi	0.0193367 psi
Millimeters of Mercury	mmHg	1 mmHg
Megapascal	MPa	0.000133322 MPa
Gigapascal	GPa	1.333220e-7 GPa
Kilopound per Square Inch	ksi	0.0000193367 ksi
Inch of Mercury	inHg	0.0393699 inHg
Kilogram-force per Square Centimeter	kgf/cm²	0.00135951 kgf/cm²

Common Uses of the Torr

•Automotive — inflating tires to manufacturer-specified pressures
•Weather reporting — tracking barometric pressure for forecasting
•Hydraulic systems — designing and operating fluid power equipment
•Scuba diving — calculating safe dive depths based on partial pressures
•Medical — measuring blood pressure and calibrating medical equipment

Did You Know?

The deepest point in the ocean — the Challenger Deep in the Mariana Trench — has a water pressure of approximately 110 MPa, or about 1,086 times standard atmospheric pressure. The Torr is one of several units used to express pressures across this extraordinary range.

Scientific Definition of the Torr

The Torr (torr) is defined within the context of pressure measurement. Modern metrology ties most measurement units to fundamental physical constants or precisely reproducible laboratory references, ensuring that a measurement made in one laboratory gives the same result as a measurement made anywhere else in the world. This traceability to international standards is what makes the Torr reliable for scientific research, commercial trade, engineering design, and legal metrology. When you use a conversion tool to translate between the Torr and other units, the underlying conversion factors are the exact ratios defined by international standards bodies — not approximations. This means the only limit to the accuracy of a conversion is the precision of your input measurement. For everyday use, converting the Torr to equivalent units in other systems is instant and accurate to many more decimal places than any practical measurement could justify.

Tips for Converting the Torr

When converting the Torr to other pressure units, pay careful attention to the direction of the conversion factor — multiplying and dividing are not interchangeable. A quick sanity check is to estimate the expected magnitude of the result before performing the conversion: if the target unit is larger than the Torr, the numerical value should be smaller, and vice versa. For chained conversions across multiple unit systems, convert everything to a common intermediate unit (typically the SI base unit) and then from that intermediate to the target. This approach is more reliable than direct conversion through multiple factors and makes the calculation easier to verify. When working with very large or very small values, consider whether a metric prefix (milli-, kilo-, mega-) would make the number easier to interpret without losing precision. For critical applications, always cross-check the converted value using a second method — a different calculator, a published table, or a hand calculation using the conversion factor directly.

Accuracy and Precision

Conversion of the Torr is performed using exact, internationally defined factors wherever possible. For units defined by historical artifact or local convention, small differences between national standards may exist — for example, the difference between US survey foot and international foot, or the subtle variations between different definitions of the BTU. These differences are usually negligible for everyday use but matter in precision engineering, legal metrology, and international scientific collaboration. The MegaCalc conversion engine uses the most current internationally accepted values and documents any edge cases where multiple definitions exist. Numerical precision of conversions is carried to at least 10 significant figures internally, with displayed results rounded to a readable length. If you need additional precision for a specific calculation, the underlying engine provides the full precision on request — just inspect the source code or contact us for details.