Convert Inch of Mercury to Kilopascal (inHg → kPa)

Converting inches of mercury to kilopascals is straightforward: multiply by the conversion factor. Follow these three steps to do it by hand or in your head.

1. 1
   Take your value in inches of mercury

   Start with the number of inches of mercury (inHg) you want to convert.
2. 2
   Multiply by 3.386389

   The conversion factor from inHg to kPa is 3.386389. Multiply your value by this number.
3. 3
   Read the result in kilopascals

   The result is your value in kilopascals (kPa).

Multiply the value in inches of mercury by 3.386389. For the reverse direction, multiply by 0.2953.

• ✓1 inHg ≈ 3386 Pa ≈ 33.86 mbar.
• ✓29.92 inHg = 1013.25 mbar = 1 atm.
• ✓US pilots use inHg; European pilots use hPa (mbar).

• ✗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.

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)

What is the Kilopascal?

The kilopascal equals 1,000 pascals and is the standard everyday pressure unit on tire labels (in metric countries), weather forecasts (often expressed as hPa or hectopascals, where 100 kPa = 1 atmosphere), and modern engineering documents. Car tire pressures are typically 200–250 kPa (29–36 psi), medical blood-pressure cuffs measure in mmHg but research increasingly uses kPa, and industrial process pressures are routinely given in kPa. The kilopascal is the most-used pressure unit in metric engineering practice, replacing the older 'kg/cm²' (kilogram-force per square centimeter, ≈ 98 kPa). It relates to the pascal (1,000 Pa = 1 kPa), the megapascal (1,000 kPa = 1 MPa), the bar (1 bar = 100 kPa), the psi (1 psi ≈ 6.895 kPa), and the atmosphere (1 atm ≈ 101.325 kPa). European tire pressure labels universally use kPa or bar.

• Tyre pressures in Canada, Australia
• Engineering pressure specs
• Weather pressure in some contexts