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 kilopascal?
A kilopascal is a metric pressure unit equal to 1,000 pascals. It is used for weather forecasts, tire pressure specifications in metric countries, and structural and mechanical engineering calculations.
Real-world uses
Kilopascals are used for tyre pressure in most countries (standard car tyres are about 200–250 kPa), blood pressure in some medical systems, and hydraulic system specifications. Atmospheric pressure at sea level is approximately 101.325 kPa.
History
The kilopascal became a practical engineering unit with the adoption of the SI system. It offers a convenient scale for everyday pressure measurements, bridging the gap between the tiny pascal and the larger bar or atmosphere.
Common mistakes
Confusing kPa with psi when checking tyre pressure. 1 psi ≈ 6.895 kPa, so 32 psi ≈ 220 kPa. Inflating a tyre to 32 kPa instead of 220 kPa would leave it nearly flat.
When is this conversion used?
Converting between inch of mercury and kilopascal 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 inch of mercury = 3.386389 kilopascal
1 kilopascal = 1,000 pascal
How to convert inch of mercury to kilopascal
To convert inch of mercury to kilopascal, multiply the value by 3.386389.
To convert kilopascal back to inch of mercury, multiply by 0.2952998.
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 kilopascal
| inch of mercury | kilopascal |
|---|---|
| 0.1 | 0.3386389 |
| 0.5 | 1.6931945 |
| 1 | 3.386389 |
| 2 | 6.772778 |
| 5 | 16.931945 |
| 10 | 33.86389 |
| 25 | 84.659725 |
| 50 | 169.31945 |
| 100 | 338.6389 |
| 250 | 846.59725 |
| 500 | 1,693.1945 |
| 1,000 | 3,386.389 |
Common values
| inch of mercury | kilopascal | |
|---|---|---|
| Car tyre | 64.96595636 inch of mercury | 220 kilopascal |
| Standard atmosphere | 29.9212524 inch of mercury | 101.325 kilopascal |
| Blood pressure (systolic) | 4.72479683 inch of mercury | 16 kilopascal |
| Deep-sea submersible | 32,482.97818118 inch of mercury | 110,000 kilopascal |
| Bicycle tyre | 183.08587702 inch of mercury | 620 kilopascal |
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