What is inch of mercury?
Inch of mercury (inHg) is a pressure unit representing the pressure exerted by a one-inch column of mercury. It is used in aviation altimetry, barometric pressure readings, and vacuum measurements in the United States.
Real-world uses
Inches of mercury are used in US aviation for altimeter settings (standard is 29.92 inHg), weather reporting on American TV broadcasts, and HVAC system vacuum measurements. American barometers are traditionally scaled in inHg.
History
Inches of mercury originate from the mercury barometer invented by Torricelli in 1644. The use of inches (rather than millimetres) reflects the Imperial measurement tradition. US aviation adopted inHg for altimeter settings, while most other countries use hPa.
Common mistakes
Confusing inches of mercury with millimetres of mercury—29.92 inHg = 760 mmHg = 1 atm. Also, assuming the conversion from inHg to psi is simple; 1 inHg ≈ 0.491 psi, not a round number.
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 inch of mercury 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.
Worked examples
1 inch of mercury = 0.00338639 megapascal
1 megapascal = 1,000,000 pascal
How to convert inch of mercury to megapascal
To convert inch of mercury to megapascal, multiply the value by 0.00338639.
To convert megapascal back to inch of mercury, multiply by 295.29980165.
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: inch of mercury to megapascal
| inch of mercury | megapascal |
|---|---|
| 0.1 | 0.00033864 |
| 0.5 | 0.00169319 |
| 1 | 0.00338639 |
| 2 | 0.00677278 |
| 5 | 0.01693195 |
| 10 | 0.03386389 |
| 25 | 0.08465973 |
| 50 | 0.16931945 |
| 100 | 0.3386389 |
| 250 | 0.84659725 |
| 500 | 1.6931945 |
| 1,000 | 3.386389 |
Common values
| inch of mercury | megapascal | |
|---|---|---|
| Car tyre | 64.96595636 inch of mercury | 0.22 megapascal |
| Standard atmosphere | 29.9212524 inch of mercury | 0.101325 megapascal |
| Blood pressure (systolic) | 4.72479683 inch of mercury | 0.016 megapascal |
| Deep-sea submersible | 32,482.97818118 inch of mercury | 110 megapascal |
| Bicycle tyre | 183.08587702 inch of mercury | 0.62 megapascal |
Available Pressure units
More inch of mercury conversions
- Convert inch of mercury to pascal
- Convert inch of mercury to kilopascal
- Convert inch of mercury to bar
- Convert inch of mercury to pound per square inch
- Convert inch of mercury to atmosphere
- Convert inch of mercury to millibar
- Convert inch of mercury to hectopascal
- Convert inch of mercury to torr
- Convert inch of mercury to megapascal