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.
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.
When is this conversion used?
Converting between pascal and inch of mercury 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 pascal = 0.0002953 inch of mercury
1 inch of mercury = 3,386.389 pascal
How to convert pascal to inch of mercury
To convert pascal to inch of mercury, multiply the value by 0.0002953.
To convert inch of mercury back to pascal, multiply by 3,386.389.
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: pascal to inch of mercury
| pascal | inch of mercury |
|---|---|
| 0.1 | 0.00002953 |
| 0.5 | 0.00014765 |
| 1 | 0.0002953 |
| 2 | 0.0005906 |
| 5 | 0.0014765 |
| 10 | 0.002953 |
| 25 | 0.0073825 |
| 50 | 0.01476499 |
| 100 | 0.02952998 |
| 250 | 0.07382495 |
| 500 | 0.1476499 |
| 1,000 | 0.2952998 |
Common values
| pascal | inch of mercury | |
|---|---|---|
| Car tyre | 220,000 pascal | 64.96595636 inch of mercury |
| Standard atmosphere | 101,325 pascal | 29.9212524 inch of mercury |
| Blood pressure (systolic) | 16,000 pascal | 4.72479683 inch of mercury |
| Deep-sea submersible | 110,000,000 pascal | 32,482.97818118 inch of mercury |
| Bicycle tyre | 620,000 pascal | 183.08587702 inch of mercury |