Convert Inch of Mercury to Pound per Square Inch (inHg → psi)
The inch of mercury is the American aviation standard for altimeter settings and historic barometer readings.
Inch of Mercury to Pound per Square Inch Conversion Table
10 common values| Inch of Mercury | Pound per Square Inch |
|---|---|
| 1 inHg | 0.491154 psi |
| 5 inHg | 2.455771 psi |
| 10 inHg | 4.911542 psi |
| 25 inHg | 12.278855 psi |
| 50 inHg | 24.55771 psi |
| 100 inHg | 49.11542 psi |
| 200 inHg | 98.23084 psi |
| 500 inHg | 245.5771 psi |
| 1,000 inHg | 491.1542 psi |
| 5,000 inHg | 2,455.771 psi |
How to Convert Inch of Mercury to Pound per Square Inch Manually
Step by StepConverting inches of mercury to psi is straightforward: multiply by the conversion factor. Follow these three steps to do it by hand or in your head.
- 1Take your value in inches of mercuryStart with the number of inches of mercury (inHg) you want to convert.
- 2Multiply by 0.491154The conversion factor from inHg to psi is 0.491154. Multiply your value by this number.
- 3Read the result in psiThe result is your value in psi (psi).
Formula
Multiply the value in inches of mercury by 0.491154. For the reverse direction, multiply by 2.036021.
psi = inHg × 0.491154inHg = psi × 2.036021Tips
Use these in everyday conversions- 1 inHg ≈ 3386 Pa ≈ 33.86 mbar.
- 29.92 inHg = 1013.25 mbar = 1 atm.
- US pilots use inHg; European pilots use hPa (mbar).
Common Mistakes
Avoid these- Confusing inHg with mmHg — factor of 25.4.
- Mixing US and European altimeter units on a single flight plan.
- Using inHg on scientific papers — prefer Pa.
About Inch of Mercury and Pound per Square Inch
What is the Inch of Mercury?
The inch of mercury equals exactly 25.4 mmHg (or about 3,386.4 pascals) and is the American aviation standard for altimeter settings and historic barometer readings. Pilots set their altimeters to the local atmospheric pressure in inHg before takeoff and landing — standard 'sea-level pressure' is 29.92 inHg. American weather reports historically used inHg before transitioning to millibars/hPa, and home barometers in the US still display inHg. The unit relates to the mmHg (25.4 mmHg = 1 inHg), the millibar (1 inHg ≈ 33.864 mbar), the kilopascal (1 inHg ≈ 3.386 kPa), and the psi (1 inHg ≈ 0.491 psi). Aviation's continued use of inHg in the United States reflects regulatory tradition rather than scientific advantage; international ATC outside the US uses hectopascals.
- US aviation altimeter QNH settings
- US residential barometers
- US weather forecasts (older)
Sea-level standard: 29.92 inHg. Mountain pass at 3000 m: ~21 inHg. US aviation QNH given in inHg.
What is the Pound per Square Inch?
Pounds per square inch (psi) equals approximately 6,895 pascals and is the standard pressure unit in American tire pressures, hydraulics, and gas-cylinder specifications. American car tires are typically inflated to 30–35 psi, household water systems run at 40–60 psi, and scuba tanks are filled to 3,000 psi (about 200 bar). The psi is essential in American engineering for stress calculations, hydraulic systems, and pneumatic equipment. Two variants exist: 'psig' (gauge, measured above atmospheric) and 'psia' (absolute, including atmosphere) — gauge is the default unless specified. The psi relates to the pascal (1 psi ≈ 6,895 Pa), the kilopascal (1 psi ≈ 6.895 kPa), the bar (14.504 psi = 1 bar), the atmosphere (14.696 psi = 1 atm), and the inch of mercury (1 inHg ≈ 0.491 psi). Outside the US, kPa or bar dominate.
- US tyre pressures
- US plumbing and water system specs
- US compressed-air tool ratings
US tyre: 32–35 psi. Water supply: 40–60 psi. SCUBA tank: 3000 psi. Car AC system: 30–200 psi.