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 pascal?
The pascal is the SI base unit of pressure, equal to one newton per square metre. It is used in meteorology, fluid dynamics, materials science, and all scientific pressure measurements.
Real-world uses
The pascal is the SI unit of pressure used in engineering stress analysis, materials science, and acoustics (sound pressure levels). Concrete and steel specifications list compressive strength in megapascals (MPa). Atmospheric pressure is about 101,325 Pa.
History
Named after Blaise Pascal, the French mathematician and physicist who conducted pioneering experiments on fluid pressure and vacuum in the 1640s. The pascal was adopted as the SI unit of pressure in 1971 at the 14th General Conference on Weights and Measures.
Common mistakes
Using pascals directly for everyday pressure is impractical since one pascal is a very small pressure (about the weight of a dollar bill spread over a desk). Most practical applications use kPa, hPa, or MPa instead.
When is this conversion used?
Converting between inch of mercury and pascal 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 = 3,386.389 pascal
1 pascal = 1 pascal
How to convert inch of mercury to pascal
To convert inch of mercury to pascal, multiply the value by 3,386.389.
To convert pascal back to inch of mercury, multiply by 0.0002953.
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 pascal
| inch of mercury | pascal |
|---|---|
| 0.1 | 338.6389 |
| 0.5 | 1,693.1945 |
| 1 | 3,386.389 |
| 2 | 6,772.778 |
| 5 | 16,931.945 |
| 10 | 33,863.89 |
| 25 | 84,659.725 |
| 50 | 169,319.45 |
| 100 | 338,638.9 |
| 250 | 846,597.25 |
| 500 | 1,693,194.5 |
| 1,000 | 3,386,389 |
Common values
| inch of mercury | pascal | |
|---|---|---|
| Car tyre | 64.96595636 inch of mercury | 220,000 pascal |
| Standard atmosphere | 29.9212524 inch of mercury | 101,325 pascal |
| Blood pressure (systolic) | 4.72479683 inch of mercury | 16,000 pascal |
| Deep-sea submersible | 32,482.97818118 inch of mercury | 110,000,000 pascal |
| Bicycle tyre | 183.08587702 inch of mercury | 620,000 pascal |
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