Torr

ScientificCurrent unit

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

1 torr = 133.3223684 pascals (approximately).

About the torr

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.

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

Torr conversion chart

1 torr expressed in every other pressure unit:

More Scientific units

• millimeter of mercury (pressure)
• millimeter of water (pressure)
• femtometer (length)
• angstrom (length)
• dalton (weight & mass)
• cubic kilometer (volume)
• barn (area)
• degree Rankine (temperature)
• degree Newton (temperature)
• picosecond (time)
• shake (time)
• Mach (speed)
• speed of light (speed)
• kilometer per second (speed)
• calorie (energy)
• kilocalorie (energy)

All Scientific units

Browse all pressure units.