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 megapascal?
A megapascal is a pressure unit equal to one million pascals. It is used for measuring high pressures in industrial hydraulics, structural materials testing, and deep-sea and geological applications.
Real-world uses
Megapascals are used for concrete compressive strength (typical structural concrete is 20–40 MPa), steel tensile strength (mild steel ≈ 250 MPa yield), and hydraulic system pressures. Geologists use MPa for rock stress and tectonic pressure at depth.
History
The megapascal became a standard engineering unit with the global adoption of SI. It provides a convenient scale for material strength and high-pressure applications, replacing older units like kgf/cm² and ksi (kilopounds per square inch) in most countries.
Common mistakes
Confusing MPa with kPa—they differ by a factor of 1,000. Specifying concrete strength as 30 kPa instead of 30 MPa would describe an impossibly weak material. Also, 1 MPa = 1 N/mm², a useful equivalence often forgotten.
When is this conversion used?
Converting between pound per square inch and megapascal 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 = 0.00689476 megapascal
1 megapascal = 1,000,000 pascal
How to convert pound per square inch to megapascal
To convert pound per square inch to megapascal, multiply the value by 0.00689476.
To convert megapascal back to pound per square inch, multiply by 145.03773773.
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 megapascal
| pound per square inch | megapascal |
|---|---|
| 0.1 | 0.00068948 |
| 0.5 | 0.00344738 |
| 1 | 0.00689476 |
| 2 | 0.01378951 |
| 5 | 0.03447379 |
| 10 | 0.06894757 |
| 25 | 0.17236893 |
| 50 | 0.34473786 |
| 100 | 0.68947573 |
| 250 | 1.72368932 |
| 500 | 3.44737865 |
| 1,000 | 6.89475729 |
Common values
| pound per square inch | megapascal | |
|---|---|---|
| Car tyre | 31.9083023 pound per square inch | 0.22 megapascal |
| Standard atmosphere | 14.69594878 pound per square inch | 0.101325 megapascal |
| Blood pressure (systolic) | 2.3206038 pound per square inch | 0.016 megapascal |
| Deep-sea submersible | 15,954.15115032 pound per square inch | 110 megapascal |
| Bicycle tyre | 89.92339739 pound per square inch | 0.62 megapascal |
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