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

Hectopascal to Inch of Mercury Conversion Formula

To convert a pressure from hectopascals (hPa) to inches of mercury (inHg), multiply by 0.02953.

• inHg = hPa × 0.02953

The factor follows from the conventional inch of mercury (3,386.39 Pa) and the hectopascal (exactly 100 Pa): 100 ÷ 3,386.39 = 0.029530. The touchstone every meteorologist knows: 1,013.25 hPa = 29.92 inHg, the standard atmosphere in both dialects.

Step-by-Step Example

A hurricane advisory reports a central pressure of 920 hPa, and a US audience expects inches of mercury:

1. Take the pressure: 920 hPa
2. Multiply by 0.02953: 920 × 0.02953 = 27.17 inHg

Divide by 0.02953 to convert the other way: a home barometer showing 30.10 inHg is reading 1,019.3 hPa.

Quick Reference Table

Two Dialects of the Same Weather

The hectopascal is the world's meteorological standard — chosen because 1 hPa equals exactly 1 millibar, letting decades of weather records carry over unchanged when the SI name was adopted. The United States is the major holdout: public forecasts, home barometers and aviation altimeter settings (with Canada) still use inches of mercury. The same physical reading therefore circulates in two dialects — a METAR from Frankfurt says Q1013 (hPa) while one from Chicago says A2992 (inHg), both describing a standard day. Anyone comparing international weather data, tracking Atlantic hurricanes (advisories quote hPa/mb even for US audiences), or flying between the two systems performs this conversion routinely. The extreme ends of the table above are not decorative: 870 hPa is the lowest sea-level pressure ever measured (Typhoon Tip, 1979) and values above 1,050 hPa occur in strong Siberian winter highs — real barometric readings span that whole range.

How many hectopascals are in one inch of mercury? One Inch of mercury (inHg) contains 33.863889532610878529 hectopascals (hPa) — the inverse of the factor above. Multiplying by 0.029529980572284863811 takes you from hectopascals to inches of mercury; multiplying by 33.863889532610878529 brings you back.

Put in words: one hectopascal equals 0.029529980572284863811 inches of mercury, so the hectopascal is the smaller unit of this pair. Converting between them never changes the amount of pressure being measured — only the size of the unit you count it in.

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).

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.

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)

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)

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.

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.

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)

hectopascal to Inch of mercury Conversion Table

Here are some quick reference conversions from hectopascal (hPa) to Inch of mercury (inHg):

This conversion in other languages

Engineering datasheets across Europe write hectopascal to Inch of mercury several different ways. The calculation is the same in every one of them.