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.
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.
When is this conversion used?
Converting millibar to hectopascal is useful in the pressure domain when comparing values across different measurement standards or applying formulas that require a specific unit.
Worked examples
1 millibar = 1 hectopascal
1 hectopascal = 100 pascal
How to convert millibar to hectopascal
To convert millibar to hectopascal, multiply the value by 1.
To convert hectopascal back to millibar, multiply by 1.
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: millibar to hectopascal
| millibar | hectopascal |
|---|---|
| 0.1 | 0.1 |
| 0.5 | 0.5 |
| 1 | 1 |
| 2 | 2 |
| 5 | 5 |
| 10 | 10 |
| 25 | 25 |
| 50 | 50 |
| 100 | 100 |
| 250 | 250 |
| 500 | 500 |
| 1,000 | 1,000 |
Common values
| millibar | hectopascal | |
|---|---|---|
| Car tyre | 2,200 millibar | 2,200 hectopascal |
| Standard atmosphere | 1,013.25 millibar | 1,013.25 hectopascal |
| Blood pressure (systolic) | 160 millibar | 160 hectopascal |
| Deep-sea submersible | 1,100,000 millibar | 1,100,000 hectopascal |
| Bicycle tyre | 6,200 millibar | 6,200 hectopascal |