What is pound per square inch?
Pound per square inch (psi) is an imperial pressure unit widely used in the United States for tire inflation, hydraulic system pressures, gas cylinder ratings, and plumbing specifications.
Real-world uses
PSI is the standard pressure unit in the United States for tyre inflation (typically 30–35 psi for cars), compressed air tools, hydraulic systems, and water pressure. HVAC systems, fire extinguisher ratings, and pressure cooker specifications use psi in North America.
History
Pounds per square inch emerged naturally from the Imperial/US customary system, combining the pound-force with the square inch. It became the dominant pressure unit in American industry and remains deeply embedded in US engineering standards and building codes.
Common mistakes
Not distinguishing between psi (absolute, psia) and psig (gauge, relative to atmosphere). A tyre reading of 32 psig actually means about 46.7 psia. Also, confusing psi with kPa when using equipment from metric countries.
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 between pound per square inch and hectopascal 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. 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 pound per square inch = 68.94757293 hectopascal
1 hectopascal = 100 pascal
How to convert pound per square inch to hectopascal
To convert pound per square inch to hectopascal, multiply the value by 68.94757293.
To convert hectopascal back to pound per square inch, multiply by 0.01450377.
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: pound per square inch to hectopascal
| pound per square inch | hectopascal |
|---|---|
| 0.1 | 6.89475729 |
| 0.5 | 34.47378647 |
| 1 | 68.94757293 |
| 2 | 137.89514586 |
| 5 | 344.73786466 |
| 10 | 689.47572932 |
| 25 | 1,723.68932329 |
| 50 | 3,447.37864658 |
| 100 | 6,894.75729317 |
| 250 | 17,236.89323292 |
| 500 | 34,473.78646584 |
| 1,000 | 68,947.57293168 |
Common values
| pound per square inch | hectopascal | |
|---|---|---|
| Car tyre | 31.9083023 pound per square inch | 2,200 hectopascal |
| Standard atmosphere | 14.69594878 pound per square inch | 1,013.25 hectopascal |
| Blood pressure (systolic) | 2.3206038 pound per square inch | 160 hectopascal |
| Deep-sea submersible | 15,954.15115032 pound per square inch | 1,100,000 hectopascal |
| Bicycle tyre | 89.92339739 pound per square inch | 6,200 hectopascal |
Available Pressure units
More pound per square inch conversions
- Convert pound per square inch to pascal
- Convert pound per square inch to kilopascal
- Convert pound per square inch to bar
- Convert pound per square inch to atmosphere
- Convert pound per square inch to millibar
- Convert pound per square inch to hectopascal
- Convert pound per square inch to torr
- Convert pound per square inch to inch of mercury
- Convert pound per square inch to megapascal