Convert Pressure from kilopascals to Inches of mercury (kPa to inHg)

Kilopascal to Inch of Mercury Conversion Formula

To convert pressure from kilopascals (kPa) to inches of mercury (inHg), multiply by 0.2953.

• inHg = kPa × 0.2953

The factor follows from the definition of the inch of mercury: a 1-inch (25.4 mm) column of mercury at 0 °C exerts 3.386389 kPa, and 1 ÷ 3.386389 = 0.295300. For quick mental arithmetic, "multiply by 0.3" gets you within 1.6%.

The anchor every pilot and meteorologist knows:

• 101.325 kPa = 29.92 inHg — standard sea-level atmosphere.

Step-by-Step Example

A Canadian weather service reports station pressure of 98.6 kPa, and a US-built altimeter needs the setting in inHg:

1. Take the pressure: 98.6 kPa
2. Multiply by 0.2953: 98.6 × 0.2953 = 29.12 inHg

Reverse direction: multiply by 3.38639 — an altimeter setting of 30.15 inHg is 102.10 kPa.

Quick Reference Table

Aviation, Weather and Vacuum — Three Homes of the inHg

This conversion sits on the border between metric and US customary practice. Aviation is the biggest user: altimeter settings are broadcast in inHg in the United States but in hectopascals (= 0.1 kPa) almost everywhere else, so crews crossing borders convert constantly — and the table above doubles as an hPa table if you multiply the kPa column by 10. Weather reporting in US media quotes barometric pressure in inHg, while scientific data arrives in kPa or hPa. Finally, HVAC and automotive vacuum work in North America measures manifold and refrigerant-line vacuum in inHg. A note for accuracy: this page uses the 0 °C (32 °F) mercury column definition, the one used in aviation and meteorology; a "60 °F inch of mercury" also exists in some US gas-industry contexts and differs by about 0.5%.

How many kilopascals are in one inch of mercury? One Inch of mercury (inHg) contains 3.3863889532610878529 kilopascals (kPa) — the inverse of the factor above. Multiplying by 0.29529980572284863811 takes you from kilopascals to inches of mercury; multiplying by 3.3863889532610878529 brings you back.

Put in words: one kilopascal equals 0.29529980572284863811 inches of mercury, so the kilopascal 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 kilopascal (kPa)?

A kilopascal (kPa) is a metric unit of pressure that equals 1,000 pascals.

It is one of the most common units for measuring pressure worldwide, used in both scientific and everyday applications.

The Kilopascal (kPa) Explained

The base unit, the pascal (Pa), is named after the French polymath Blaise Pascal.

As part of the metric system (also known as the SI system), the kilopascal is widely used in scientific, engineering, and industrial fields due to its standardization and ease of calculation.

Common Applications of Kilopascals (kPa)

The kPa unit is used to measure pressure in many everyday and technical contexts. Common examples include:

• Tire Pressure: A common measurement for vehicle tire pressure in many countries outside the US.
• Weather Forecasting: Used for reporting atmospheric pressure.
• HVAC Systems: Essential for measuring differential pressure in heating, ventilation, and air conditioning systems.
• Medical: Frequently used for measuring blood pressure.
• Manufacturing: Critical for monitoring pressure in various industrial processes.

Kilopascal Conversions (kPa to PSI and Bar)

For practical use, it's essential to understand how kPa converts to other common pressure units.

• kPa to PSI: 1 kPa is approximately 0.145 PSI (Pounds per Square Inch). PSI is the standard pressure unit used in the United States.
• kPa to Bar: 100 kPa is exactly equal to 1 bar. The bar is another metric unit frequently used for atmospheric and water pressure.

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)

kilopascal to Inch of mercury Conversion Table

Here are some quick reference conversions from kilopascal (kPa) to Inch of mercury (inHg):

This conversion in other languages

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