Torr to Atm Converter
Convert between torr, atmospheres, pascals, and millimeters of mercury. Enter values for instant results with step-by-step formulas.
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Formula
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.
Last reviewed: December 2025
Worked Examples
Example 1: Laboratory Vacuum Conversion
Example 2: Boiling Point at Altitude
Background & Theory
The Torr to Atm Converter applies the following established principles and formulas. Unit conversion is the process of expressing a quantity in a different unit of measurement while preserving its physical meaning. At the foundation of modern measurement lies the International System of Units (SI), which defines seven base units: the meter for length, kilogram for mass, second for time, ampere for electric current, kelvin for thermodynamic temperature, mole for amount of substance, and candela for luminous intensity. All other units, called derived units, are defined as algebraic combinations of these seven. Dimensional analysis is the principal method for performing unit conversions. By treating units as algebraic quantities that can be multiplied, divided, and cancelled, a conversion factor chain allows a value expressed in one unit to be rewritten in another without altering its physical magnitude. For example, to convert 60 miles per hour to meters per second, one multiplies by a chain of conversion factors each equal to one: (1609.34 m / 1 mile) × (1 hour / 3600 s). Metric prefixes enable compact expression of quantities across extreme ranges of magnitude. Standard prefixes span from nano (10^-9) through micro (10^-6) and milli (10^-3) up through kilo (10^3), mega (10^6), and giga (10^9), and beyond in both directions. These prefixes are strictly multiplicative and apply consistently to any SI base or derived unit. Temperature conversions require affine transformations rather than simple scaling. To convert Celsius to Fahrenheit the formula is °F = (°C × 9/5) + 32, while the conversion to the absolute Kelvin scale is K = °C + 273.15. These formulas reflect the different zero points and degree-size conventions of each scale. Significant figures govern how precision is preserved through calculations. A result should not express more precision than the least precise input value permits. In digital storage, IEEE and IEC standards distinguish between decimal prefixes (kilobyte = 1000 bytes) and binary prefixes (kibibyte = 1024 bytes), a distinction that has practical consequences for how storage capacity is reported by manufacturers versus operating systems. Unit coherence — ensuring that all quantities in an equation share a consistent unit system — is essential for obtaining correct results.
History
The history behind the Torr to Atm Converter traces back through the following developments. Human beings have been measuring and comparing quantities since before recorded history. The earliest known measurement units were body-based: the cubit (the distance from elbow to fingertip), the foot, the hand, and the digit. The furlong originated as the length of a furrow a team of oxen could plow without resting. These anthropomorphic standards were practical for local use but differed between regions and kingdoms, creating persistent difficulties in trade and construction. The ancient Egyptians standardized the royal cubit at approximately 52.4 centimeters and distributed calibrated granite rods to ensure consistency across building projects, including the pyramids. Roman engineers used the mile (mille passuum, one thousand double paces) and spread these standards throughout their empire via road networks. Despite these efforts, measurement diversity persisted across medieval Europe, hampering commerce. The French Revolution created political will for radical standardization. In 1795 France officially adopted the metric system, defining the meter as one ten-millionth of the distance from the equator to the North Pole along the Paris meridian. This gave the world its first fully decimal, rationally constructed measurement system. The Metre Convention of 1875 established the International Bureau of Weights and Measures (BIPM) in Sevres, France, creating a permanent international body to maintain physical artifact standards and coordinate global metrology. For over a century, the kilogram was defined by a platinum-iridium cylinder locked in a vault near Paris. In 1999, a stark demonstration of what unit inconsistency costs occurred when NASA's Mars Climate Orbiter was lost because one engineering team used pound-force seconds while another used newton seconds. The spacecraft entered the Martian atmosphere at the wrong angle and was destroyed, at a cost of 327 million dollars. In 2019 the SI underwent its most significant revision, redefining all seven base units in terms of fixed numerical values of fundamental physical constants such as the speed of light, Planck's constant, and the elementary charge. This eliminated any reliance on physical artifacts and made the measurement system permanently stable and universally reproducible.
Frequently Asked Questions
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\nPascals = 50 x 133.322 = 6,666.1 Pa\nkPa = 6,666.1 / 1,000 = 6.6661 kPa\nPSI = 6,666.1 / 6,894.76 = 0.9668 PSI\nBar = 6,666.1 / 100,000 = 0.06666 bar\nmmHg = 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\nPascals = 630 x 133.322 = 83,992.9 Pa\nkPa = 83,992.9 / 1,000 = 83.993 kPa\nPSI = 83,992.9 / 6,894.76 = 12.183 PSI\nBar = 83,992.9 / 100,000 = 0.8399 bar\ninHg = 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.
References
Reviewed by Manoj Kumar, Mathematics Educator · Editorial policy