Pilot tools
hPa to inHg converter
Convert an altimeter setting between hectopascals and inches of mercury. Type in either box and the other fills in, to the precision you would set it at.
Also called millibars (mb). Standard is 1013
The US and Canada. Standard is 29.92
Altimeter setting
29.91inHg
Set to two decimals, as an inHg altimeter is.
- Inches of mercury
- 29.91inHg
- Hectopascals
- 1013hPa
- From standard
- -0.3hPa
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For flight simulation only. Don't use it for real-world flight planning or navigation.
How it works
Both units measure the same thing: air pressure at sea level, as the altimeter needs it. A hectopascal (hPa) is the metric unit, and one hectopascal is one millibar (mb). An inch of mercury (inHg) is the pressure of a column of mercury an inch high, which is 33.8639 hPa.
inHg = hPa ÷ 33.8639
hPa = inHg × 33.8639
Set an inHg altimeter to two decimals, so 1013 hPa is 29.91. Hectopascals are set in whole numbers, and the working above keeps one decimal.
Standard pressure is 1013.25 hPa, or 29.92 inHg. You set it when you climb through the transition altitude, so every aircraft at flight level uses the same reference, and you go back to the local pressure (QNH) from the airport weather when you descend through the transition level. The US and Canada give the setting in inHg; most other countries use hPa. Our Mach to knots converter covers the other number that changes with altitude.
Questions
How do you convert hPa to inHg?
Divide the pressure in hectopascals by 33.8639. For 1013 hPa that is 1013 ÷ 33.8639 = 29.91 inHg. To go the other way, multiply inches of mercury by 33.8639: 29.92 inHg × 33.8639 = 1013.2 hPa.
What is standard pressure in hPa and inHg?
Standard pressure is 1013.25 hPa, which is 29.92 inHg. Pilots round it to 1013 hPa when they set it, and the altimeter setting to 29.92 inHg.
Is hPa the same as mb?
Yes. One hectopascal is exactly one millibar, so 1013 hPa and 1013 mb are the same pressure. Hectopascal is the official unit; some pilots and older charts still say millibars.
When do I set the altimeter to standard pressure?
When you climb through the transition altitude, you set 1013 hPa (29.92 inHg) and fly flight levels from there. When you descend through the transition level, you set the local pressure (QNH) from the airport weather or ATIS. The transition altitude varies by country: 18,000 ft in the United States and 10,000 ft in Australia, for example.
Which countries use inHg and which use hPa?
The United States and Canada give the altimeter setting in inches of mercury, such as 29.92. Most other countries give QNH in hectopascals, such as 1013. A METAR shows the difference: "A2992" is 29.92 inHg and "Q1013" is 1013 hPa.
What is QNH?
QNH is the altimeter setting that makes your altimeter read your height above mean sea level. It's the local pressure, adjusted down to sea level, so it changes with the weather, and you get it from ATC or the ATIS.
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