mm Hg to ATM Converter
Enter a pressure in millimeters of mercury (mmHg) to get the equivalent in standard atmospheres (atm) plus five other common pressure units: kilopascals, pascals, bar, psi, and Torr. Switch the direction to convert from atm back to mmHg. The conversion uses the exact definition: 1 atm = 760 mmHg at 0 degrees Celsius at sea level.
What is the mmHg to atm conversion?
Millimeters of mercury (mmHg) and standard atmospheres (atm) are both units for measuring pressure. The conversion is exact by definition: 1 standard atmosphere equals exactly 760 millimeters of mercury at 0 degrees Celsius and standard gravity (9.80665 m/s squared). To convert mmHg to atm, divide the value by 760. To convert atm to mmHg, multiply by 760. For example, 380 mmHg equals 0.5 atm, and 1,520 mmHg equals 2 atm.
Where are these pressure units used?
Millimeters of mercury originated from the classic mercury barometer, where atmospheric pressure was measured by the height of a mercury column it could support. Today, mmHg remains the standard unit in medicine for blood pressure and intraocular pressure (normal blood pressure is about 120/80 mmHg). Meteorologists sometimes report barometric pressure in mmHg, though most now prefer hectopascals (hPa). Standard atmospheres (atm) are widely used in chemistry, physics, and engineering to express pressures near ambient conditions. They appear frequently in gas law problems, scuba diving depth calculations, and industrial process specifications.
Pressure equivalents in other units
One standard atmosphere equals exactly 760 mmHg, 101,325 Pa, 101.325 kPa, 1.01325 bar, and approximately 14.696 psi. The Torr is a related unit nearly equal to 1 mmHg: 1 Torr = 101,325/760 Pa, making 1 mmHg equal to about 1.000000142 Torr. In everyday work the two are used interchangeably, but they differ in definition - mmHg is defined in terms of mercury density and gravity, while the Torr is defined purely from the SI pascal. This calculator converts mmHg to atm, kPa, Pa, bar, psi, and Torr simultaneously so you get all common equivalents in one step.
Practical examples in science and medicine
In chemistry, gas law problems (Boyle's, Charles's, and the ideal gas law) often express pressure in atm because many textbook values of the gas constant R use atm as the pressure unit. Converting a measured mmHg reading to atm before plugging into PV=nRT avoids unit errors. In medicine, blood pressure cuffs report in mmHg and oxygen partial pressures in arterial blood are given in mmHg (normal arterial PaO2 is about 75-100 mmHg, equal to 0.099-0.132 atm). In diving, pressures at depth are expressed in atm: every 10 metres of seawater adds roughly 1 atm, corresponding to 760 additional mmHg.
Common pressure values: mmHg to atm
| mmHg | atm | kPa | Context |
|---|---|---|---|
| 0 | 0.000000 | 0.000 | Perfect vacuum |
| 1 | 0.001316 | 0.133 | 1 mmHg (unit reference) |
| 80 | 0.105263 | 10.666 | Diastolic blood pressure (typical) |
| 120 | 0.157895 | 15.999 | Systolic blood pressure (typical) |
| 380 | 0.500000 | 50.662 | Half standard atmosphere |
| 525 | 0.690789 | 69.994 | Pressure at ~4,000 m altitude |
| 760 | 1.000000 | 101.325 | Standard atmosphere (1 atm, sea level) |
| 800 | 1.052632 | 106.661 | Slightly above standard atmosphere |
| 1013 | 1.332895 | 135.062 | Approximate surface of Venus |
| 1520 | 2.000000 | 202.650 | Two standard atmospheres |
Reference conversions for frequently encountered pressures in science, medicine, and meteorology.
Frequently asked questions
How do I convert mmHg to atm?
Divide the pressure in mmHg by 760. The conversion factor is exact: 1 standard atmosphere is defined as exactly 760 millimeters of mercury. For example, 380 mmHg / 760 = 0.5 atm, and 1,140 mmHg / 760 = 1.5 atm.
How do I convert atm to mmHg?
Multiply the pressure in atm by 760. For example, 2.5 atm x 760 = 1,900 mmHg. Use the direction toggle in this calculator to switch from mmHg-to-atm to atm-to-mmHg mode.
Is mmHg the same as Torr?
Nearly, but not exactly. The Torr is defined as exactly 101,325/760 Pa, while the millimeter of mercury is based on the physical properties of mercury (density 13,595.1 kg/m3 at 0 degrees Celsius) and standard gravity. The difference is about 0.000014%, so for virtually all practical purposes 1 mmHg = 1 Torr. Scientific publications in vacuum technology and spectroscopy use Torr; medical literature uses mmHg.
What is standard atmospheric pressure in mmHg?
Standard atmospheric pressure is exactly 760 mmHg by definition (equivalent to 101,325 Pa, 101.325 kPa, or 1.01325 bar). Actual atmospheric pressure at sea level varies with weather, typically ranging from about 720 to 800 mmHg.
Why is blood pressure measured in mmHg?
The mercury sphygmomanometer, invented in the late 19th century, measured how high blood pressure could push a column of mercury. The mmHg unit stuck because of this historical instrument, and international standards still specify blood pressure in mmHg even though modern digital cuffs contain no mercury. Normal resting blood pressure is approximately 120 mmHg systolic and 80 mmHg diastolic (written 120/80 mmHg), equivalent to about 0.158 and 0.105 atm respectively.
What is 760 mmHg in other pressure units?
760 mmHg = 1 atm = 101,325 Pa = 101.325 kPa = 1.01325 bar = 14.696 psi = 760 Torr (approximately). This set of equivalencies is the foundation of most pressure unit conversions and is exact for atm, Pa, kPa, and bar by SI definition.