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Torr to Inch of Mercury Converter

Convert torr to inches of mercury with our free online pressure converter.

Quick Answer

1 Torr = 0.03937 inches of mercury

Formula: Torr × conversion factor = Inch of Mercury

Use the calculator below for instant, accurate conversions.

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All conversion formulas on UnitsConverter.io have been verified against NIST (National Institute of Standards and Technology) guidelines and international SI standards. Our calculations are accurate to 10 decimal places for standard conversions and use arbitrary precision arithmetic for astronomical units.

Last verified: February 2026Reviewed by: Sam Mathew, Software Engineer

Torr to Inch of Mercury Calculator

How to Use the Torr to Inch of Mercury Calculator:

  1. Enter the value you want to convert in the 'From' field (Torr).
  2. The converted value in Inch of Mercury will appear automatically in the 'To' field.
  3. Use the dropdown menus to select different units within the Pressure category.
  4. Click the swap button (⇌) to reverse the conversion direction.
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How to Convert Torr to Inch of Mercury: Step-by-Step Guide

Converting Torr to Inch of Mercury involves multiplying the value by a specific conversion factor, as shown in the formula below.

Formula:

inHg = Torr × 0.0393701

Example Calculation:

1 Torr = 0.03937 inHg

Disclaimer: For Reference Only

These conversion results are provided for informational purposes only. While we strive for accuracy, we make no guarantees regarding the precision of these results, especially for conversions involving extremely large or small numbers which may be subject to the inherent limitations of standard computer floating-point arithmetic.

Not for professional use. Results should be verified before use in any critical application. View our Terms of Service for more information.

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📋 Unit Symbols

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What is a Torr and a Inch of Mercury?

The Torr (symbol: Torr) is a unit of pressure based on an absolute scale. It is not an SI unit, but it is widely used in science and engineering.

The Modern Definition: 1 Torr is defined as exactly 1/760 of a standard atmosphere (1 atm).

Since a standard atmosphere is defined as exactly 101,325 Pascals (Pa), the exact value of one Torr is: 1 Torr = 101,325 / 760 Pascals ≈ 133.322368421 Pascals.

** Torr vs. mmHg**: Historically, the Torr was intended to be same as the millimeter of mercury (mmHg). However, because the density of mercury changes with temperature and local gravity varies across the Earth, the mmHg is not a "true" absolute unit. To solve this, the Torr was redefined as a fixed fraction of an atmosphere, making it a perfectly stable unit regardless of where or the temperature at which you measure it.

Key standard relationships:

  • 1 Torr = 1,000 milliTorr (mTorr)
  • 760 Torr = 1 standard atmosphere (atm)
  • 1 Torr ≈ 1.333 millibars (mbar)
  • 1 Torr ≈ 0.0193 PSI (pounds per square inch)

1 inHg = 3,386.39 Pa = 3.386 kPa = 33.86 mbar = 33.86 hPa = 0.491 PSI = 0.0334 bar = 0.0334 atm = 25.4 mmHg

Key relationship: 29.92 inHg = 1 atmosphere (exactly)

Origin: Mercury Column

The unit literally measures how high mercury rises:

  • Historical: Barometers invented in 1600s used mercury column
  • Measurement: Mercury rises/falls with atmospheric pressure
  • 1 inHg: Mercury column exactly 1 inch high
  • 29.92 inHg: Mercury rises 29.92 inches at sea level (1 atm)
  • Why mercury?: Highest density liquid (narrow barometer), visible, stable

Note: The Torr is part of the imperial/US customary system, primarily used in the US, UK, and Canada for everyday measurements. The Inch of Mercury belongs to the imperial/US customary system.

History of the Torr and Inch of Mercury

: From the First Barometer to Modern Vacuums

The history of the Torr is the history of our understanding of the "void" and the air around us.

1. Evangelista Torricelli and the "Sea of Air" (1643)

Before the 1640s, scientists believed that "nature abhors a vacuum" and that space was always filled with something. Evangelista Torricelli, a student of Galileo, challenged this. He filled a glass tube with mercury and inverted it into a bowl. Instead of all the mercury flowing out, it stopped at a height of about 76 cm (760 mm).

Torricelli correctly deduced that it wasn't a "pull" from the vacuum at the top of the tube, but the weight of the atmosphere pushing down on the mercury in the bowl that held the liquid up. He famously stated: "We live submerged at the bottom of an ocean of elementary air."

2. The Birth of the Name (1913)

For centuries, pressure was simply measured in "inches of mercury" or "millimeters of mercury." In 1913, the unit was formally named the Torr to honor Torricelli.

3. The Great Redefinition (1954)

As science became more precise, the variance in mercury density became a problem (a "millimeter of mercury" in the Arctic was technically different from one at the Equator). In 1954, at the 10th General Conference on Weights and Measures, the Standard Atmosphere was fixed at exactly 101,325 Pascals. Consequently, the Torr was redefined as exactly 1/760 of that value, decoupling it from the physical properties of mercury forever.

Common Uses and Applications: torr vs inches of mercury

Explore the typical applications for both Torr (imperial/US) and Inch of Mercury (imperial/US) to understand their common contexts.

Common Uses for torr

When to Use inches of mercury

US Weather: Barometric pressure in weather forecasts, NOAA reports - THE US standard. Aviation: Altimeter settings (US standard, some international - critical for flight safety). HVAC: Vacuum measurements, duct pressure, system diagnostics. Historical meteorology: Traditional US measurement since early 1900s.

Additional Unit Information

About Torr (Torr)

What is the difference between Torr and mmHg?

For almost all practical, medical, and industrial purposes, they are the same. However, scientifically:

  • Torr is defined as exactly 1/760 of a Standard Atmosphere (Standardized in 1954).
  • mmHg (millimeter of mercury) is based on the actual weight of liquid mercury, which changes slightly depending on gravity and temperature.
  • The difference is 1 part in 7 million. Unless you are building a particle accelerator, you can treat them as identical.

Why is Torr used in vacuum technology?

Torr is the preferred unit because most vacuum systems are based on pumping down from atmospheric pressure. Since 760 Torr is a standard atmosphere, it's very easy for an engineer to know how "far" they have to go. It also uses a logarithmic scale naturally, making it easy to talk about 10⁻⁶ or 10⁻⁹ Torr levels.

Is a Torr a "Metric" unit?

No. The official SI unit for pressure is the Pascal (Pa). However, because 1 Pascal is such a small amount of pressure (about the weight of a dollar bill on a table), scientists in specific fields prefer the Torr for convenience.

How do you convert Torr to PSI?

Multiply your Torr value by 0.0193368. Formula: PSI = Torr × 0.0193368 Example: 100 Torr ≈ 1.93 PSI.

What is a "milliTorr" (mTorr)?

Also known as a Micron, a milliTorr is 1/1,000th of a Torr. It is commonly used in "roughing" vacuum pumps (like the one in your school's physics lab or a high-end food sealer).

Is 0 Torr possible?

A "perfect" vacuum (exactly 0 Torr) is theoretically impossible according to quantum mechanics. Even in deep intergalactic space, there is a pressure of about 10⁻¹⁷ Torr due to a few stray hydrogen atoms and cosmic radiation.

Is Torr used in the medical field?

Yes, but doctors almost always call it mmHg. When a nurse says your blood pressure is "120 over 80," they are literally saying "120 Torr systolic and 80 Torr diastolic."

Who is the unit Torr named after?

It is named after Evangelista Torricelli, the Italian physicist who proved that air has weight and invented the mercury barometer in 1643.

How many Pascals are in a Torr?

Exactly 133.322368... Pascals. For most calculations, using 133.3 is sufficient.

What happens if you are exposed to 0 Torr?

This is "space vacuum." Contrary to movies, your head doesn't explode. However, the oxygen in your blood would diffuse out of your lungs into the vacuum, causing you to lose consciousness in about 15 seconds. Your skin is tough enough to hold "you" together, but you would swell up significantly as water in your tissues starts to turn to gas.

About Inch of Mercury (inHg)

How do I convert inHg to PSI?

Formula: PSI = inHg × 0.491154

Examples:

  • 29.92 inHg = 14.7 PSI (sea level)
  • 30 inHg = 14.74 PSI
  • 28 inHg = 13.75 PSI (hurricane)
  • 25 inHg = 12.28 PSI
  • 20 inHg = 9.82 PSI

inHg to PSI converter →

How many inHg is normal atmospheric pressure?

Standard sea level = 29.92 inHg (exactly 1 atmosphere)

Typical weather range: 29.4-30.5 inHg

Pressure variations:

  • High pressure: 30.2-30.5 inHg (fair weather)
  • Normal: 29.8-30.2 inHg
  • Low pressure: 29.4-29.8 inHg (rain likely)
  • Storm: <29.4 inHg

Barometer rising/falling:

  • Rising: Improving weather
  • Steady: Conditions stable
  • Falling: Weather deteriorating

How do I convert inHg to mbar or hPa?

Formula: mbar (or hPa) = inHg × 33.8639

Examples:

  • 29.92 inHg = 1,013.25 mbar = 1,013.25 hPa (standard)
  • 30.0 inHg = 1,016 mbar
  • 29.0 inHg = 982 mbar (low pressure)
  • 28.0 inHg = 948 mbar (hurricane)
  • 31.0 inHg = 1,050 mbar (high pressure)

inHg to mbar converter → inHg to hPa converter →

Why does US use inHg instead of mbar/hPa?

Historical: US adopted imperial/customary units Mercury barometers: Traditionally marked in inches in US Weather tradition: NOAA, Weather Channel use inHg since inception Familiarity: Public knows "normal is about 30 inches" Aviation: US pilots trained with inHg altimeter settings

Rest of world: Uses mbar or hPa (metric standard)

Conversion: 30 inHg ≈ 1,000 mbar (approximately)

Trend: Slow transition—some US reports now show both units

How do I read a mercury barometer in inHg?

How it works: Mercury column rises/falls with atmospheric pressure

Reading:

  • Look at top of mercury meniscus (curved surface)
  • Read scale at eye level to avoid parallax error
  • Scale typically 28-31 inHg range

Interpreting:

  • 30.2-30.5 inHg: High pressure (fair, clear weather)
  • 29.8-30.2 inHg: Normal (stable conditions)
  • 29.4-29.8 inHg: Low pressure (clouds, possible rain)
  • <29.4 inHg: Very low (storm likely)

Trend matters: Falling rapidly = weather worsening; Rising = improving

Adjustment: Correct for altitude (sea level reading)

Conversion Table: Torr to Inch of Mercury

Torr (Torr)Inch of Mercury (inHg)
0.50.02
10.039
1.50.059
20.079
50.197
100.394
250.984
501.969
1003.937
2509.843
50019.685
1,00039.37

People Also Ask

How do I convert Torr to Inch of Mercury?

To convert Torr to Inch of Mercury, enter the value in Torr in the calculator above. The conversion will happen automatically. Use our free online converter for instant and accurate results. You can also visit our pressure converter page to convert between other units in this category.

Learn more →

What is the conversion factor from Torr to Inch of Mercury?

The conversion factor depends on the specific relationship between Torr and Inch of Mercury. You can find the exact conversion formula and factor on this page. Our calculator handles all calculations automatically. See the conversion table above for common values.

Can I convert Inch of Mercury back to Torr?

Yes! You can easily convert Inch of Mercury back to Torr by using the swap button (⇌) in the calculator above, or by visiting our Inch of Mercury to Torr converter page. You can also explore other pressure conversions on our category page.

Learn more →

What are common uses for Torr and Inch of Mercury?

Torr and Inch of Mercury are both standard units used in pressure measurements. They are commonly used in various applications including engineering, construction, cooking, and scientific research. Browse our pressure converter for more conversion options.

For more pressure conversion questions, visit our FAQ page or explore our conversion guides.

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All Pressure Conversions

Pascal to KilopascalPascal to MegapascalPascal to HectopascalPascal to BarPascal to MillibarPascal to AtmospherePascal to Technical AtmospherePascal to TorrPascal to Millimeter of MercuryPascal to Inch of MercuryPascal to Pound per Square InchPascal to Kilopound per Square InchPascal to Kilogram-force per Square CentimeterPascal to Kilogram-force per Square MeterPascal to Millimeter of Water ColumnPascal to Inch of Water ColumnKilopascal to PascalKilopascal to MegapascalKilopascal to HectopascalKilopascal to BarKilopascal to MillibarKilopascal to AtmosphereKilopascal to Technical AtmosphereKilopascal to TorrKilopascal to Millimeter of MercuryKilopascal to Inch of MercuryKilopascal to Pound per Square InchKilopascal to Kilopound per Square InchKilopascal to Kilogram-force per Square CentimeterKilopascal to Kilogram-force per Square MeterKilopascal to Millimeter of Water ColumnKilopascal to Inch of Water ColumnMegapascal to PascalMegapascal to KilopascalMegapascal to HectopascalMegapascal to BarMegapascal to MillibarMegapascal to AtmosphereMegapascal to Technical AtmosphereMegapascal to TorrMegapascal to Millimeter of MercuryMegapascal to Inch of MercuryMegapascal to Pound per Square InchMegapascal to Kilopound per Square InchMegapascal to Kilogram-force per Square CentimeterMegapascal to Kilogram-force per Square MeterMegapascal to Millimeter of Water ColumnMegapascal to Inch of Water ColumnHectopascal to PascalHectopascal to KilopascalHectopascal to MegapascalHectopascal to BarHectopascal to MillibarHectopascal to AtmosphereHectopascal to Technical AtmosphereHectopascal to TorrHectopascal to Millimeter of MercuryHectopascal to Inch of MercuryHectopascal to Pound per Square InchHectopascal to Kilopound per Square InchHectopascal to Kilogram-force per Square CentimeterHectopascal to Kilogram-force per Square MeterHectopascal to Millimeter of Water ColumnHectopascal to Inch of Water ColumnBar to PascalBar to KilopascalBar to MegapascalBar to HectopascalBar to MillibarBar to AtmosphereBar to Technical AtmosphereBar to TorrBar to Millimeter of MercuryBar to Inch of MercuryBar to Pound per Square InchBar to Kilopound per Square InchBar to Kilogram-force per Square CentimeterBar to Kilogram-force per Square MeterBar to Millimeter of Water ColumnBar to Inch of Water ColumnMillibar to PascalMillibar to KilopascalMillibar to MegapascalMillibar to HectopascalMillibar to BarMillibar to AtmosphereMillibar to Technical AtmosphereMillibar to TorrMillibar to Millimeter of MercuryMillibar to Inch of MercuryMillibar to Pound per Square InchMillibar to Kilopound per Square InchMillibar to Kilogram-force per Square CentimeterMillibar to Kilogram-force per Square MeterMillibar to Millimeter of Water ColumnMillibar to Inch of Water ColumnAtmosphere to PascalAtmosphere to KilopascalAtmosphere to MegapascalAtmosphere to HectopascalAtmosphere to BarAtmosphere to MillibarAtmosphere to Technical AtmosphereAtmosphere to TorrAtmosphere to Millimeter of MercuryAtmosphere to Inch of MercuryAtmosphere to Pound per Square InchAtmosphere to Kilopound per Square InchAtmosphere to Kilogram-force per Square CentimeterAtmosphere to Kilogram-force per Square MeterAtmosphere to Millimeter of Water ColumnAtmosphere to Inch of Water ColumnTechnical Atmosphere to PascalTechnical Atmosphere to KilopascalTechnical Atmosphere to MegapascalTechnical Atmosphere to HectopascalTechnical Atmosphere to BarTechnical Atmosphere to MillibarTechnical Atmosphere to AtmosphereTechnical Atmosphere to Torr

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Verified Against Authority Standards

All conversion formulas have been verified against international standards and authoritative sources to ensure maximum accuracy and reliability.

NIST Reference on Constants, Units and Uncertainty

National Institute of Standards and Technology — Fundamental physical constants and unit conversions

BIPM SI Units

Bureau International des Poids et Mesures — International System of Units (SI) definitions and standards

ISO 80000

International Organization for Standardization — Quantities and units international standards series

Last verified: February 19, 2026