Torr to Atm Converter
Convert between torr, atmospheres, pascals, and millimeters of mercury. Enter values for instant results with step-by-step formulas.
Reviewed for accuracy by Manoj Kumar, Mathematics Educator
Formula
ATM = Torr / 760
One standard atmosphere equals exactly 760 torr. The torr is defined as 1/760 of an atmosphere, making 1 torr = 133.322 pascals. Torr and mmHg are nearly identical (differing by less than 0.000015%), and are often used interchangeably in scientific work.
Worked Examples
Example 1: Laboratory Vacuum Conversion
Problem:A rotary evaporator is operating at 50 torr vacuum. Express this pressure in atm, kPa, and PSI.
Solution:ATM = 50 / 760 = 0.06579 atm Pascals = 50 x 133.322 = 6,666.1 Pa kPa = 6,666.1 / 1,000 = 6.6661 kPa PSI = 6,666.1 / 6,894.76 = 0.9668 PSI Bar = 6,666.1 / 100,000 = 0.06666 bar mmHg = 50 x 0.9999999 = 50.00 mmHg
Result:50 torr = 0.0658 atm = 6.666 kPa = 0.967 PSI = 0.0667 bar
Example 2: Boiling Point at Altitude
Problem:At an elevation where atmospheric pressure is 630 torr, determine the pressure in other units for lab calculations.
Solution:ATM = 630 / 760 = 0.8289 atm Pascals = 630 x 133.322 = 83,992.9 Pa kPa = 83,992.9 / 1,000 = 83.993 kPa PSI = 83,992.9 / 6,894.76 = 12.183 PSI Bar = 83,992.9 / 100,000 = 0.8399 bar inHg = 630 x 0.03937 = 24.80 inHg
Result:630 torr = 0.829 atm = 83.99 kPa = 12.18 PSI (water boils at ~96.5 degrees C)
Frequently Asked Questions
What is a torr and how is it defined?
A torr is a unit of pressure named after Evangelista Torricelli, the Italian physicist who invented the mercury barometer in 1644. One torr is defined as exactly 1/760 of a standard atmosphere, which makes it approximately equal to 133.322 pascals. The torr is very nearly identical to the millimeter of mercury (mmHg), differing by less than 0.000015 percent. Originally, the torr was defined as the pressure exerted by a 1-millimeter column of mercury at standard gravity and 0 degrees Celsius. The torr is extensively used in vacuum science, laboratory chemistry, and physics experiments, particularly for measuring low pressures in vacuum systems and scientific instruments.
How many torr are in one atmosphere?
One standard atmosphere equals exactly 760 torr. This definition is precise and fundamental to the torr unit, as the torr was specifically defined as 1/760 of an atmosphere. In other equivalent units, one atmosphere also equals 101,325 pascals, 1.01325 bar, 14.696 PSI, 760.000 mmHg, and 29.921 inches of mercury. The value of 760 comes from the original mercury barometer measurements, where standard atmospheric pressure supports a mercury column approximately 760 millimeters tall at sea level and 0 degrees Celsius. This relationship provides a convenient and intuitive way to express pressures in laboratory and industrial settings.
What is the difference between torr and mmHg?
Torr and mmHg are nearly identical but technically different units. The torr is defined as exactly 1/760 of a standard atmosphere (101,325 pascals), making one torr equal to 133.32236842 pascals. The mmHg is defined as the pressure exerted by a 1-mm column of mercury at 0 degrees Celsius under standard gravity (9.80665 m/s squared), making one mmHg equal to 133.32239 pascals. The difference is approximately 0.000015 percent, which is negligible for virtually all practical applications. In everyday scientific usage, torr and mmHg are treated as interchangeable. The distinction only matters in metrology and the most precise calibration work.
Where is the torr unit most commonly used?
The torr is primarily used in vacuum science and technology, where it provides convenient numbers for the pressure ranges commonly encountered. Rough vacuum ranges from 760 torr down to about 1 torr, medium vacuum from 1 torr to 0.001 torr, high vacuum from 0.001 torr to a billionth of a torr, and ultra-high vacuum below that level. The torr is also widely used in chemistry laboratories for reporting vapor pressures, in thin-film deposition processes, in mass spectrometry, and in semiconductor manufacturing where precise vacuum conditions are critical. Medical applications still use mmHg (essentially interchangeable with torr) for blood pressure measurements and respiratory pressure readings.
How do I convert torr to pascals?
To convert torr to pascals, multiply the torr value by 133.322. For example, 760 torr equals 760 times 133.322 = 101,325 pascals (which is one standard atmosphere). For kilopascals, divide the pascal result by 1,000, so 760 torr equals 101.325 kPa. For the reverse conversion, divide pascals by 133.322 to get torr. This conversion is important when working between traditional laboratory units (torr) and the SI system (pascals). In many scientific publications, pressure must be reported in SI units, requiring researchers to convert their torr-based measurements to pascals or kilopascals for publication.
What is vacuum pressure and how is it measured in torr?
Vacuum pressure refers to pressures below atmospheric pressure (760 torr at sea level). Vacuum levels are categorized as follows: low or rough vacuum ranges from 760 to 25 torr, medium vacuum from 25 to 0.001 torr, high vacuum from 0.001 to one-billionth torr, ultra-high vacuum below one-billionth torr, and extreme high vacuum below one-trillionth torr. Different measurement instruments are needed for different ranges: Bourdon gauges work above 10 torr, thermocouple gauges from 1 to 0.001 torr, ionization gauges from 0.001 to one-billionth torr. Achieving and maintaining vacuum requires increasingly sophisticated equipment as the pressure decreases, with ultra-high vacuum systems requiring baked stainless steel chambers and turbomolecular pumps.
How does vapor pressure relate to torr measurements?
Vapor pressure is the pressure exerted by a vapor in equilibrium with its liquid or solid phase at a given temperature, and it is commonly expressed in torr. Water has a vapor pressure of 23.76 torr at 25 degrees Celsius and 760 torr at 100 degrees Celsius (its boiling point at sea level). Boiling occurs when a liquid vapor pressure equals the surrounding atmospheric pressure. This is why water boils at lower temperatures at high altitudes where atmospheric pressure is less than 760 torr. In chemistry, vapor pressure data in torr helps predict evaporation rates, determines distillation conditions, and is essential for calculating solution properties using Raoult law and related thermodynamic relationships.
Who was Evangelista Torricelli and why is the unit named after him?
Evangelista Torricelli (1608-1647) was an Italian physicist and mathematician who served as a student and secretary to Galileo Galilei. In 1644, Torricelli invented the mercury barometer, the first instrument capable of measuring atmospheric pressure. His experiment involved filling a tube with mercury, inverting it in a dish of mercury, and observing that the mercury column fell to approximately 760 mm, with a vacuum forming above it. This experiment proved that the atmosphere has weight and exerts pressure, overturning the prevailing Aristotelian notion that nature abhors a vacuum. The unit torr was named in his honor to recognize this groundbreaking contribution to pressure measurement and atmospheric science.
How do altitude and weather affect torr readings?
Atmospheric pressure decreases with altitude at roughly 26.4 torr per 1,000 feet of elevation gain near sea level. At 5,280 feet (Denver), atmospheric pressure averages about 621 torr instead of the sea-level 760 torr. Weather systems also cause significant variations: high-pressure systems can produce readings of 775 to 790 torr at sea level, while strong hurricanes can drive pressure below 690 torr. The lowest recorded sea-level pressure was approximately 637 torr (870 mbar) during Typhoon Tip in 1979. These pressure variations are important for laboratory work because experimental conditions specified at 760 torr must be adjusted when working at different altitudes or during extreme weather events.
What instruments are used to measure pressure in torr?
Several instrument types measure pressure in torr across different ranges. Mercury manometers are the classic instrument, directly measuring pressure as the height of a mercury column and accurate from about 1 to 1500 torr. Capacitance diaphragm gauges (Baratron gauges) measure 0.001 to 1000 torr by detecting diaphragm deflection. Pirani gauges use thermal conductivity changes in gas to measure 0.001 to 10 torr. Thermocouple gauges cover similar ranges using a different thermal principle. Hot and cold cathode ionization gauges measure ultra-low pressures from one-billionth to 0.001 torr. Modern digital pressure transducers can display readings in torr, pascals, bar, or other units simultaneously with accuracies of 0.05 to 0.25 percent of reading.
References
Reviewed for accuracy by Manoj Kumar, Mathematics Educator ยท Editorial policy
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