Torr to Millimeters Of Mercury (Torr to mmHg)

1 torr equals 0.9999998575 millimeters of mercury (rounded).

1 torr = 0.9999998575 millimeters of mercury

How to convert torr to millimeters of mercury

To convert torr to millimeters of mercury, multiply the number of torr by 0.9999998575. The factor is rounded to 10 significant digits. To go the other way, multiply millimeters of mercury by 1.000000142 (rounded).

millimeters of mercury = torr × 0.9999998575

Example: 10 torr = 9.999998575 millimeters of mercury.

About these units

Torr (Torr)

ScientificCurrent unit

Exactly 1/760 of a standard atmosphere (about 133.322 Pa), named after Evangelista Torricelli. Used for vacuum measurement.

In 1643 Evangelista Torricelli filled a meter-long tube, sealed at one end, with mercury and stood it in a basin of mercury. The column fell to about 76 cm and left a Torricellian vacuum above it, the first recorded creation of a permanent vacuum. In a letter dated 11 June 1644 he described living at the bottom of a sea of air, an idea that also explained why suction pumps could raise water only about 10 meters.

The torr honors him. It was originally meant to equal one millimeter of mercury at 0 degrees Celsius, but the weight of a mercury column varies with gravity, which changes with elevation and latitude. In 1954 the 10th CGPM defined the standard atmosphere as 101,325 Pa, and the torr was then fixed as exactly one 760th of that, about 133.32 Pa.

Today the torr is mostly met in high-vacuum physics and engineering. It differs from the millimeter of mercury by less than one part in seven million, so the two are interchangeable except in the most exacting work.

1 torr = 133.3223684 pascals (approximately).

Sources: Wikipedia: Torr; Wikipedia: Evangelista Torricelli; Wikipedia: Standard atmosphere (unit)

Millimeter Of Mercury (mmHg)

ScientificCurrent unit

About 133.322 pascals, the pressure from a 1 mm column of mercury. Blood pressure is still reported in mmHg.

Where the torr honors a person, the millimeter of mercury describes a gauge. It is a manometric unit: originally the pressure from a mercury column 1 mm tall, which means it depends on an assumed fluid density and on gravity. Mercury manometers were among the first accurate pressure gauges, and 17th-century experiments by Torricelli and then Pascal, whose mercury stood at about 23 inches on a mountaintop against about 26 at its base, showed that air has weight and that pressure drops with altitude.

To remove the ambiguity, mmHg is now fixed at exactly 133.322387415 Pa, using a conventional mercury density of 13,595.1 kg per cubic meter and standard gravity. The torr, defined as one 760th of a standard atmosphere, differs from it by only about 0.000015 percent.

Mercury is toxic and its readings vary with temperature and local gravity, so mercury gauges are now used less, and the unit's use is discouraged. Medicine nonetheless keeps it, especially for blood pressure, which is reported relative to atmospheric pressure, and hypertension guidelines in the US and Europe still use it.

1 millimeter of mercury = 133.3223874 pascals (approximately).

Sources: Wikipedia: Millimetre of mercury; Wikipedia: Torr; Wikipedia: Blaise Pascal

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