What is torr?
A torr is a pressure unit equal to approximately 1/760 of an atmosphere. It is used in vacuum technology, low-pressure experimental physics, and blood pressure measurement in older clinical literature.
Real-world uses
Torr is used in vacuum technology, semiconductor manufacturing, and blood pressure measurement (mmHg ≈ torr). Vacuum chambers for electron beam welding operate at about 10⁻⁵ torr, and freeze-drying processes typically operate at 0.1–1 torr.
History
Named after Evangelista Torricelli, who invented the mercury barometer in 1644. The torr was defined to approximate the pressure exerted by 1 mm of mercury. It was formally standardized as 1/760 of a standard atmosphere.
Common mistakes
Assuming torr and mmHg are exactly the same—they are nearly identical but differ by about 0.000015%. For most purposes they are interchangeable, but ultra-precise vacuum work may require distinction.
What is millibar?
A millibar is a pressure unit equal to one thousandth of a bar. It is the standard unit for atmospheric pressure in meteorology and weather forecasting, particularly in aviation and marine contexts.
Real-world uses
Millibars are the traditional unit in meteorology for reporting atmospheric pressure, particularly in weather maps and hurricane tracking. Standard atmospheric pressure is 1013.25 mbar, and tropical cyclones can have central pressures below 900 mbar.
History
The millibar was introduced by Sir Napier Shaw in 1909 for meteorological use. It dominated weather reporting throughout the 20th century. Since 1982, the WMO has officially recommended hectopascals instead, though both represent exactly 100 Pa.
Common mistakes
Not realizing that 1 millibar = 1 hectopascal exactly. Meteorological services have largely switched to hPa, but the numerical values are identical. Also, assuming lower millibar values mean calmer weather—lower pressure often indicates storms.
When is this conversion used?
Converting between torr and millibar is common when working across metric and imperial systems, such as international trade, travel between countries with different measurement standards, or following instructions from a different region.
Worked examples
1 torr = 1.33322368 millibar
1 millibar = 100 pascal
How to convert torr to millibar
To convert torr to millibar, multiply the value by 1.33322368.
To convert millibar back to torr, multiply by 0.75006168.
Measurement standards
The pascal (Pa) is the SI derived unit of pressure, defined as one newton per square metre. The World Meteorological Organization mandates the hectopascal (hPa) for atmospheric pressure reporting in aviation and weather services.
Did you know?
The pressure at the bottom of the Mariana Trench, nearly 11 km deep, exceeds 1,086 bar — over a thousand times atmospheric pressure. At this depth, water is compressed by about 5%, making it measurably denser than at the surface.
Quick reference: torr to millibar
| torr | millibar |
|---|---|
| 0.1 | 0.13332237 |
| 0.5 | 0.66661184 |
| 1 | 1.33322368 |
| 2 | 2.66644737 |
| 5 | 6.66611842 |
| 10 | 13.33223684 |
| 25 | 33.33059211 |
| 50 | 66.66118421 |
| 100 | 133.32236842 |
| 250 | 333.30592105 |
| 500 | 666.61184211 |
| 1,000 | 1,333.22368421 |
Common values
| torr | millibar | |
|---|---|---|
| Car tyre | 1,650.13570195 torr | 2,200 millibar |
| Standard atmosphere | 760 torr | 1,013.25 millibar |
| Blood pressure (systolic) | 120.00986923 torr | 160 millibar |
| Deep-sea submersible | 825,067.85097429 torr | 1,100,000 millibar |
| Bicycle tyre | 4,650.38243276 torr | 6,200 millibar |