Convert Pressure from Inches of mercury to hectopascals (inHg to hPa)

What is an Inch of Mercury (inHg)?

An inch of mercury, often abbreviated as inHg, is a unit of pressure.

It is not part of the standard metric (SI) system but is widely used in the United States and in specific fields like meteorology and aviation.

The unit is defined by its name: it is the amount of pressure exerted by a column of liquid mercury exactly one inch tall at a standard temperature.

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Where is inHg Used?

You will most commonly encounter inches of mercury in a few key areas:

• Weather Reporting: In the U.S., inHg is the standard unit for reporting barometric pressure (also known as atmospheric pressure).
  A "high" pressure system indicating clear weather might be around 30.50 inHg, while a "low" pressure system associated with storms could be 28.50 inHg.

• Aviation: This measurement is critical for pilot safety.
  Pilots use the local barometric pressure (in inHg) to calibrate their altimeters—instruments that measure altitude—to ensure they are flying at the correct height.

• Vacuum Systems: The unit is also widely used in science and industry to measure vacuum pressure.
  This is common in systems like air conditioning, refrigeration, and for monitoring the manifold pressure in piston engines.

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How to Convert inHg to Other Pressure Units

Because inHg is not a global standard, it's often necessary to convert it to other pressure units for calculations or international use.

Here are the most common conversions for 1 inHg:

• 0.491154 pounds per square inch (PSI)
• 33.86 millibars (mbar)
• 3,386.39 pascals (Pa)
• 0.000491154 kilopound per square inch (ksi)

What is a hectopascal (hPa)?

A hectopascal (hPa) is a metric unit used to measure pressure.

You will most commonly see it in weather reports to describe atmospheric pressure (also known as barometric pressure).

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Hectopascal vs. Millibar: Which is it?

If you've seen millibars (mbar) on older weather maps, the hectopascal is its modern replacement.

The switch was simple for meteorologists because the units are exactly the same (1 hPa = 1 mbar).

The hectopascal is now the international standard for measuring atmospheric pressure, making weather data consistent worldwide.

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How to Convert Hectopascals to Pascals (hPa to Pa)

The conversion is in the name. The prefix "hecto-" means 100. This makes the math simple:

• 1 hectopascal (hPa) = 100 pascals (Pa)

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How to Convert Hectopascals to Kilopascals (hPa to kPa)

Just as "hecto-" means 100, "kilo-" means 1,000. This defines their relationship:

• 1 hectopascal (hPa) = 0.1 kilopascals (kPa)
• 10 hectopascals (hPa) = 1 kilopascal (kPa)