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 atmosphere?
An atmosphere (atm) is a pressure unit equal to mean atmospheric pressure at sea level, approximately 101,325 pascals. It is used as a reference in chemistry, diving tables, and altitude calculations.
Real-world uses
Atmospheres are used as a reference pressure in chemistry (standard conditions: 1 atm, 25°C), scuba diving (each 10 m of seawater adds about 1 atm), and high-pressure industrial applications like autoclaves and pressure vessels.
History
The standard atmosphere was originally defined as the pressure exerted by a 760 mm column of mercury at 0°C under standard gravity. Evangelista Torricelli first measured atmospheric pressure in 1644 using a mercury barometer, establishing this foundational concept.
Common mistakes
Confusing standard atmosphere (101,325 Pa) with technical atmosphere (1 kgf/cm² ≈ 98,066.5 Pa). Also, assuming atmospheric pressure is constant at 1 atm everywhere—it varies with altitude, weather, and temperature.
When is this conversion used?
Tyre pressure gauges, HVAC systems, and industrial equipment may use different pressure units depending on the manufacturer and region. Converting between psi, bar, and kPa is common in automotive and engineering work.
Worked examples
1 hectopascal = 0.00098692 atmosphere
1 atmosphere = 101,325 pascal
How to convert hectopascal to atmosphere
To convert hectopascal to atmosphere, multiply the value by 0.00098692.
To convert atmosphere back to hectopascal, multiply by 1,013.25.
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 atmosphere
| hectopascal | atmosphere |
|---|---|
| 0.1 | 0.00009869 |
| 0.5 | 0.00049346 |
| 1 | 0.00098692 |
| 2 | 0.00197385 |
| 5 | 0.00493462 |
| 10 | 0.00986923 |
| 25 | 0.02467308 |
| 50 | 0.04934616 |
| 100 | 0.09869233 |
| 250 | 0.24673082 |
| 500 | 0.49346163 |
| 1,000 | 0.98692327 |
Common values
| hectopascal | atmosphere | |
|---|---|---|
| Car tyre | 2,200 hectopascal | 2.17123119 atmosphere |
| Standard atmosphere | 1,013.25 hectopascal | 1 atmosphere |
| Blood pressure (systolic) | 160 hectopascal | 0.15790772 atmosphere |
| Deep-sea submersible | 1,100,000 hectopascal | 1,085.61559339 atmosphere |
| Bicycle tyre | 6,200 hectopascal | 6.11892425 atmosphere |