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Inch of Mercury Conversion Table
This comprehensive inch of mercury conversion table shows how various units relate to inHg. Use this reference for quick conversions between inch of mercury and other common pressure units.
| Conversion | To Unit | Multiplier |
|---|---|---|
| InHg to Pascals | Pascals | 3386.39 |
| InHg to Kilopascals | Kilopascals | 3.38639 |
| InHg to Bar | Bar | 0.0338639 |
| InHg to Millibar | Millibar | 33.8639 |
| InHg to Atmospheres | Atmospheres | 0.0334211 |
| InHg to Torr | Torr | 25.4 |
| InHg to PSI | PSI | 0.491154 |
| InHg to cmH₂O | Centimeters of Water | 34.5315 |
This inch of mercury conversion reference table provides accurate conversion factors for both metric and imperial pressure units. All values are based on internationally recognized standards for maximum precision in scientific and engineering applications.
What is Inch of Mercury (inHg)?
Inch of mercury (inHg) is a non-SI unit of pressure defined as the pressure exerted by a column of mercury one inch high at 0°C under standard gravity. It is commonly used in meteorology, aviation, and refrigeration systems. The unit is particularly useful for measuring atmospheric pressure and vacuum levels.
In scientific contexts, 1 inHg is defined as exactly 3,386.389 pascals. This definition is based on the density of mercury and the standard acceleration due to gravity. Our inHg conversion tool helps you easily convert between inch of mercury and other pressure units. For example, standard atmospheric pressure is approximately 29.92 inHg.
Where is Inch of Mercury Used?
Inch of mercury is primarily used in several specialized fields due to its convenient scale for measuring low pressures and pressure differences:
- Meteorology: Atmospheric pressure is often reported in inHg, especially in the United States. Standard sea level pressure is 29.92 inHg.
- Aviation: Aircraft altimeters are calibrated to show altitude based on inHg for pressure settings. Pilots adjust their altimeters using inHg readings.
- Refrigeration: Vacuum levels in refrigeration systems are often measured in inHg to ensure proper system operation.
- Industrial Processes: Various manufacturing processes that require vacuum conditions use inHg as a measurement standard.
Applications of Inch of Mercury Measurements
Inch of mercury measurements are critical in several industries and applications:
Weather Forecasting
Meteorologists use barometers that measure atmospheric pressure in inHg to predict weather changes. A falling pressure reading often indicates approaching storms.
Aircraft Altimetry
Pilots set their altimeters to local sea level pressure in inHg to get accurate altitude readings, which is critical for safe aircraft operations.
Vacuum Systems
HVAC technicians and engineers measure vacuum levels in refrigeration and industrial systems using inHg to ensure proper operation.
Medical Equipment
Certain medical devices and procedures require precise pressure measurements in inHg, particularly in respiratory and cardiovascular applications.
History of Inch of Mercury
The inch of mercury unit originates from the mercury barometer invented by Evangelista Torricelli in 1643. This device used a glass tube filled with mercury inverted into a mercury reservoir, creating a vacuum at the top of the tube. Atmospheric pressure would support a column of mercury, with its height indicating the pressure.
The use of mercury in pressure measurement became standard due to its high density, which allowed for compact instruments, and its predictable thermal expansion properties. When the imperial system was formalized, the inch of mercury became a defined unit. Today, modern pressure instruments have largely replaced mercury barometers for safety reasons, but the unit remains in common use, particularly in aviation and meteorology in the United States.
Frequently Asked Questions
How do you convert inHg to other pressure units?
Use our inHg conversion calculator above, or multiply by the appropriate conversion factor. For example, to convert inHg to psi, multiply by 0.491154; to convert inHg to pascals, multiply by 3,386.39. For detailed instructions on converting inHg to atmospheres, visit our inHg to atm converter.
What is standard atmospheric pressure in inHg?
Standard atmospheric pressure is defined as exactly 29.92 inches of mercury (inHg) at sea level and 15°C (59°F). This value is used as a reference in meteorology and aviation for calibrating pressure instruments and altimeters.
Why is inHg used in aviation?
In aviation, inHg is used because it provides a convenient scale for measuring atmospheric pressure variations that affect aircraft performance and navigation. Altimeters are calibrated in inHg, allowing pilots to set local sea level pressure and obtain accurate altitude readings. This is essential for safe aircraft separation and landing operations.
Is inHg an SI unit?
No, inHg is not an SI unit. The SI unit for pressure is the pascal (Pa). However, inHg is still widely used in practical applications, particularly in the United States, due to historical precedent and its convenient scale for measuring atmospheric pressures.
What's the difference between inHg and mmHg?
Both units measure pressure based on mercury columns, but they differ in scale. One inch of mercury (inHg) equals exactly 25.4 millimeters of mercury (mmHg). In medical contexts, mmHg is more common (e.g., blood pressure), while inHg is prevalent in meteorology and aviation.
How precise are inHg measurements?
Modern electronic pressure sensors can measure inHg with high precision, typically to 0.01 inHg or better. However, traditional mercury barometers were limited to about 0.01 inHg by the resolution of the scale. For most practical applications, this level of precision is sufficient.
Can inHg measure vacuum pressures?
Yes, inHg is commonly used to measure vacuum pressures. In refrigeration and HVAC systems, vacuum levels are often expressed in "inches of mercury vacuum," where higher values indicate deeper vacuums. For example, a vacuum of 29.92 inHg represents a perfect vacuum at sea level.
Is your inHg conversion tool free to use?
Yes, our inch of mercury conversion calculator is completely free with no registration required. Simply enter your value, select your target unit, and get instant, accurate results. We believe precise pressure conversion should be accessible to everyone, from students learning about pressure units to professionals working on HVAC systems.