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Inch of Mercury to Atmosphere Converter

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

Quick Answer

1 Inch of Mercury = 0.033421 atmospheres

Formula: Inch of Mercury × conversion factor = Atmosphere

Use the calculator below for instant, accurate conversions.

Our Accuracy Guarantee

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

Inch of Mercury to Atmosphere Calculator

How to Use the Inch of Mercury to Atmosphere Calculator:

  1. Enter the value you want to convert in the 'From' field (Inch of Mercury).
  2. The converted value in Atmosphere 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 Inch of Mercury to Atmosphere: Step-by-Step Guide

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

Formula:

atm = inHg × 0.0334211

Example Calculation:

1 inHg = 0.033421 atm

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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What is a Inch of Mercury and a Atmosphere?

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

1 atm = 101,325 Pa = 101.325 kPa = 14.696 PSI = 1.01325 bar = 760 mmHg = 760 Torr = 29.92 inHg

Why "Atmosphere"?

The atmosphere unit is uniquely important because:

  • Defined exactly: CIPM (1954) set 1 atm = 101,325 Pa (exact)
  • Sea level reference: Based on average atmospheric pressure (not variable)
  • Universal constant: Used identically worldwide (unlike PSI or bar)
  • Chemistry standard: All chemistry/physics equations reference 1 atm conditions
  • STP baseline: "Standard Temperature and Pressure" = 0°C, 1 atm exactly

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

Common Uses and Applications: inches of mercury vs atmospheres

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

Common Uses for 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.

When to Use atmospheres

Chemistry: Gas laws (PV=nRT), reaction conditions, vapor pressures, standard conditions (STP).

  • Ideal Gas Law: P V = n R T (pressures typically in atm in chemistry)
  • Gas tables: Vapor pressures often given at 1 atm
  • STP (Standard Temperature & Pressure): Exactly 1 atm, 0°C (sometimes 25°C modern definition)

Diving: Depth pressure calculations (1 atm per 10m/33ft water).

  • Critical for: Decompression sickness risk, nitrogen narcosis, oxygen toxicity
  • Rule of thumb: Every 10 meters adds 1 atm pressure

Physics: Standard reference pressure for equations, thermodynamics.

  • Thermodynamics: Heat capacities typically defined at 1 atm
  • Boiling points: Water boils at 100°C only at 1 atm
  • Phase diagrams: Reference state for matter phase transitions

Engineering: High-pressure systems, pressure vessels, gas storage.

  • Vessel ratings: Designed for X psig over 1 atm ambient
  • Cylinder classifications: Based on working pressure as multiples of atm

Additional Unit Information

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)

About Atmosphere (atm)

How many PSI is 1 atmosphere?

1 atm = 14.696 PSI (often rounded to 14.7 PSI)

Examples:

  • 2 atm = 29.4 PSI (10m dive depth)
  • 3 atm = 44.1 PSI (20m dive depth)
  • 10 atm = 147 PSI (compressed air)
  • 100 atm = 1,470 PSI (gas cylinder)

Atmosphere to PSI converter →

How many atmospheres in a bar?

1 bar = 0.986923 atm (approximately 1 atm, ~1.3% difference)

Conversion:

  • 1 atm = 1.01325 bar
  • 10 atm = 10.1325 bar
  • 100 atm = 101.325 bar
  • 200 atm = 202.65 bar (scuba tank)

Why different?: Bar defined as exactly 100,000 Pa; atm defined as 101,325 Pa.

Atmosphere to Bar converter →

What pressure is 2 atmospheres?

2 atm = 202,650 Pa = 202.65 kPa = 29.4 PSI = 2.026 bar = 1,520 mmHg

Physical meaning:

  • Diving 10 meters (33 feet) underwater
  • Absolute pressure at 10m depth
  • Double the surface atmospheric pressure
  • Pressure inside a pressure cooker

How do I calculate diving depth pressure?

Formula: Total Pressure (atm) = 1 + (Depth in meters ÷ 10)

Or: Total Pressure (atm) = 1 + (Depth in feet ÷ 33)

Examples:

  • 10m (33ft): 1 + (10÷10) = 2 atm
  • 20m (66ft): 1 + (20÷10) = 3 atm
  • 30m (99ft): 1 + (30÷10) = 4 atm
  • 40m (131ft): 1 + (40÷10) = 5 atm

Note: Freshwater calculation uses 10.3m; saltwater 10m per atmosphere.

What is STP in chemistry?

STP (Standard Temperature and Pressure):

  • Pressure: 1 atm = 101,325 Pa = 100 kPa (IUPAC uses 100 kPa)
  • Temperature: 0°C = 273.15 K

Purpose: Reference conditions for gas law calculations

Molar volume at STP: 22.414 L/mol (IUPAC: 22.711 L/mol at 100 kPa)

SATP (Standard Ambient):

  • Pressure: 1 atm = 101,325 Pa
  • Temperature: 25°C = 298.15 K
  • Molar volume: 24.465 L/mol

More commonly used in modern chemistry.

Conversion Table: Inch of Mercury to Atmosphere

Inch of Mercury (inHg)Atmosphere (atm)
0.50.017
10.033
1.50.05
20.067
50.167
100.334
250.836
501.671
1003.342
2508.355
50016.711
1,00033.421

People Also Ask

How do I convert Inch of Mercury to Atmosphere?

To convert Inch of Mercury to Atmosphere, enter the value in Inch of Mercury 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 Inch of Mercury to Atmosphere?

The conversion factor depends on the specific relationship between Inch of Mercury and Atmosphere. 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 Atmosphere back to Inch of Mercury?

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

Learn more →

What are common uses for Inch of Mercury and Atmosphere?

Inch of Mercury and Atmosphere 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