What is hectopascal?
A hectopascal is a pressure unit equal to 100 pascals, numerically identical to the millibar. It is the standard unit for atmospheric pressure reports in modern meteorology and aviation weather data.
Real-world uses
Hectopascals are the modern meteorological standard for atmospheric pressure reporting, used by the World Meteorological Organization and most national weather services. Standard atmospheric pressure is 1013.25 hPa. Altimeter settings in aviation outside the US use hPa (QNH).
History
The hectopascal was promoted by the WMO beginning in 1982 as a replacement for the millibar, aligning meteorology with the SI system. Since 1 hPa equals exactly 1 mbar, the transition required no changes to numerical readings or instruments.
Common mistakes
Not realizing that 1 hPa = 1 mbar exactly. The switch from millibars to hectopascals changed only the name, not the numerical values. Also, some people confuse hPa with kPa; 1 kPa = 10 hPa.
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.
When is this conversion used?
Converting between hectopascal and torr 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 hectopascal = 0.75006168 torr
1 torr = 133.32236842 pascal
How to convert hectopascal to torr
To convert hectopascal to torr, multiply the value by 0.75006168.
To convert torr back to hectopascal, multiply by 1.33322368.
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: hectopascal to torr
| hectopascal | torr |
|---|---|
| 0.1 | 0.07500617 |
| 0.5 | 0.37503084 |
| 1 | 0.75006168 |
| 2 | 1.50012337 |
| 5 | 3.75030841 |
| 10 | 7.50061683 |
| 25 | 18.75154207 |
| 50 | 37.50308414 |
| 100 | 75.00616827 |
| 250 | 187.51542068 |
| 500 | 375.03084135 |
| 1,000 | 750.0616827 |
Common values
| hectopascal | torr | |
|---|---|---|
| Car tyre | 2,200 hectopascal | 1,650.13570195 torr |
| Standard atmosphere | 1,013.25 hectopascal | 760 torr |
| Blood pressure (systolic) | 160 hectopascal | 120.00986923 torr |
| Deep-sea submersible | 1,100,000 hectopascal | 825,067.85097429 torr |
| Bicycle tyre | 6,200 hectopascal | 4,650.38243276 torr |