Convert Pressure from Inches of mercury to millimeters of mercury (inHg to mmHg)

Inch of mercury to millimeter of mercury Conversion Formula

Example

Let's convert 5 Inch of mercury (inHg) to millimeter of mercury (mmHg).

Using the formula:

Therefore, 5 Inch of mercury (inHg) is equal to 127.00038077965706534 millimeter of mercury (mmHg).

How many inches of mercury are in one millimeter of mercury? One millimeter of mercury (mmHg) contains 0.039369960698581626129 Inches of mercury (inHg) — the inverse of the factor above. Multiplying by 25.400076155931413067 takes you from inches of mercury to millimeters of mercury; multiplying by 0.039369960698581626129 brings you back.

Put in words: one inch of mercury equals 25.400076155931413067 millimeters of mercury, so the inch of mercury is the larger 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 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)

What Is a Millimeter of Mercury (mmHg)?

A millimeter of mercury (mmHg) is a manometric unit of pressure.

It was historically defined as the pressure generated by a column of mercury exactly one millimeter high.

Today, it is most famous as the unit used in medicine for measuring blood pressure. It is also commonly used in meteorology, aviation, and physics to measure atmospheric pressure or vacuum pressure.

The Origin of the mmHg Unit

The mmHg unit originates from the invention of the barometer by Evangelista Torricelli in 1643.

Torricelli's device measured atmospheric pressure by seeing how high it could support a column of mercury in a tube.

Standard atmospheric pressure was found to support a column approximately 760 mm high, which established 760 mmHg as a standard reference point.

Common Applications of mmHg

The most well-known application of mmHg is in medicine.

• Blood Pressure: Readings are given as two numbers: systolic pressure (when the heart beats) over diastolic pressure (when the heart rests), such as 120/80 mmHg. This is a critical vital sign for human health.

• Meteorology: Used for reporting barometric (atmospheric) pressure, which helps in weather forecasting.

• Physics & Engineering: Used for measuring vacuum pressures and other low-pressure systems where precision is needed.

How to Convert mmHg to Other Pressure Units

While mmHg is common, other pressure units are standard in different fields. Here are the most common conversions:

• 1 mmHg = 133.322 pascals (Pa)
• 1 mmHg = 0.133322 kilopascals (kPa)
• 760 mmHg = 1 standard atmosphere (atm)

Inch of mercury to millimeter of mercury Conversion Table

Here are some quick reference conversions from Inch of mercury (inHg) to millimeter of mercury (mmHg):