Torr to Atm Conversion
Convert pressure between Torr, ATM, Pascal, PSI, bar, and more. Instant bidirectional pressure unit conversion.
Torr to Atm Conversion
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Formula: ATM = Torr / 760 | Pa = Torr x 133.322
Worked example — 0.5 Torr = 0.000658 atm = 66.661 Pa
Formula
ATM = Torr / 760 | Pa = Torr x 133.322
One standard atmosphere equals exactly 760 Torr. All conversions route through Pascals (the SI unit): multiply the input by its Pascal factor, then divide by the target unit Pascal factor. For example, Torr to atm: multiply by 133.322 to get Pascals, then divide by 101325 to get atmospheres.
Worked Examples
Example 1: Vacuum System Reading
Problem:A vacuum pump achieves 0.5 Torr. Express this in atm and Pa.
Solution:atm = Torr / 760 = 0.5 / 760 = 0.000658 atm Pa = Torr x 133.322 = 0.5 x 133.322 = 66.661 Pa This is a medium vacuum level, suitable for many industrial processes.
Result:0.5 Torr = 0.000658 atm = 66.661 Pa
Example 2: Blood Pressure Conversion
Problem:Systolic blood pressure is 120 mmHg (Torr). Convert to kPa and psi.
Solution:kPa = Torr x 0.133322 = 120 x 0.133322 = 15.999 kPa psi = Torr x (133.322 / 6894.76) = 120 x 0.01934 = 2.320 psi atm = 120 / 760 = 0.1579 atm
Result:120 Torr = 16.0 kPa = 2.32 psi = 0.158 atm
Frequently Asked Questions
How do you convert Torr to ATM?
To convert Torr to atmospheres, divide the Torr value by 760. This is because one standard atmosphere is defined as exactly 760 Torr (or 760 mmHg). For example, 380 Torr equals 0.5 atm (380 / 760 = 0.5). The Torr unit was named after Evangelista Torricelli, who invented the mercury barometer in 1644 and demonstrated that atmospheric pressure supports a column of mercury approximately 760 mm high at sea level.
What is the difference between Torr and mmHg?
Torr and millimeters of mercury (mmHg) are nearly identical but have a subtle technical difference. The Torr is defined as exactly 1/760 of a standard atmosphere (101325 Pa / 760 = 133.322 Pa), while mmHg is based on the actual physical height of a mercury column under specific conditions of gravity and temperature. In practice the difference is less than 0.000015%, so they are used interchangeably in most applications including medical blood pressure readings and vacuum system measurements.
When is the Torr unit typically used?
Torr is most commonly used in vacuum science and technology, where pressures range from rough vacuum (a few hundred Torr) down to ultra-high vacuum (less than one billionth of a Torr). It is also used in blood pressure measurements as mmHg (for example 120/80 mmHg), in meteorology for barometric pressure, and in chemistry for vapor pressure measurements. The unit is particularly convenient because standard atmospheric pressure is the easy-to-remember value of 760 Torr.
What is standard atmospheric pressure in different units?
Standard atmospheric pressure (sea level, 15 degrees C) is defined as exactly 101,325 Pascals. This equals 1 atm, 760 Torr, 1.01325 bar, 1013.25 mbar (or hPa), 14.696 psi, 29.921 inches of mercury, and 760 mmHg. These values are fundamental reference points in physics, engineering, and meteorology. Weather reports often use millibars or hectopascals, while tire pressures use psi or bar, and scientific work typically uses Pascals or Torr.
How do you convert Torr into PSI?
Route the value through the standard atmosphere. One atmosphere is exactly 760 Torr and 14.6959 psi, so one Torr equals 14.6959 / 760 = 0.0193368 psi. Converting 500 Torr therefore gives 500 x 0.0193368 = 9.67 psi, and the reverse divides psi by that factor. Because these units are all absolute-scale definitions, no offset term is needed, only a multiplication.
What is the difference between absolute and gauge pressure?
Absolute pressure is measured from a perfect vacuum, while gauge pressure is measured relative to the surrounding atmosphere, so gauge equals absolute minus ambient. Torr and atm are normally quoted as absolute values, which is why vacuum work uses them, whereas psi often appears as psig on tyre and compressor gauges. Local barometric pressure must be added back whenever a gauge reading feeds into a Torr conversion.
How does the millibar used in weather reporting relate to Torr?
Standard sea-level pressure is 1013.25 mbar and 760 Torr, so one Torr equals 1.33322 mbar and one millibar equals 0.750062 Torr. The millibar is numerically identical to the hectopascal, which is why meteorological charts print hPa and mbar interchangeably. A barometer reading of 1000 mbar is therefore about 750 Torr, slightly below the standard atmosphere.
What is a micron of mercury and where is it used?
A micron in vacuum work means one micrometre of mercury column, which is one millitorr, or 0.001 Torr. It is the working unit on HVAC and refrigeration vacuum gauges, where an evacuation target is quoted in hundreds of microns to show that moisture and non-condensable gases have been drawn out. Since 760,000 microns equals one atmosphere, the scale expresses deep vacuum without long strings of decimal places.
Why is the pascal the SI unit rather than the atmosphere?
The pascal is coherent with the rest of SI: it is one newton per square metre, built from base units without an arbitrary reference. The atmosphere is instead a defined constant fixed at exactly 101,325 Pa, and the Torr is defined as one seven-hundred-and-sixtieth of that. Calculations involving force, area or energy stay dimensionally clean in pascals, so conversion routines normally pass every unit through Pa as the pivot.
Which pressure unit suits vacuum work versus pressurised piping?
Torr and millitorr suit vacuum systems because the interesting range spans many decades below atmospheric and the numbers stay readable. Bar and psi suit pressurised process piping, where readings sit above ambient and gauge scales dominate. Pascals or kilopascals are the safest choice for published calculations because they carry no reference-atmosphere assumption and no ambiguity between US and imperial conventions.
References
Reviewed for accuracy by Manoj Kumar, Mathematics Educator · Editorial policy
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