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Inch of Mercury to Hectopascal Converter

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

Quick Answer

1 Inch of Mercury = 33.86389 hectopascals

Formula: Inch of Mercury × conversion factor = Hectopascal

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 Hectopascal Calculator

How to Use the Inch of Mercury to Hectopascal Calculator:

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

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

Formula:

hPa = inHg × 33.8639

Example Calculation:

1 inHg = 33.86389 hPa

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 Hectopascal?

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 hPa = 100 Pa = 0.1 kPa = 1 mbar (exactly) = 0.001 bar = 0.0145 PSI = 0.000987 atm = 0.75 mmHg

Why Hectopascal?

The hectopascal perfectly bridges SI and traditional meteorology:

  • SI compliance: Uses SI base unit (Pascal)
  • Backward compatibility: 1 hPa = 1 mbar exactly (no conversion needed)
  • Convenient scale: Typical atmospheric pressure ~1,000 hPa (manageable numbers)
  • Global adoption: WMO (World Meteorological Organization) standard since 1980s

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 Hectopascal belongs to the imperial/US customary system.

History of the Inch of Mercury and Hectopascal

: The Transition from Millibar

The Evolution of Pressure Units

  • Pre-1900s: Mercury column (mmHg) standard for all pressure
  • 1900s-1980s: Meteorologists adopted millibar (mbar = 1/1000 bar)
    • Why: Sea level pressure ~1,013 mbar (convenient round number)
    • Advantage: Easy to work with 3-4 digit numbers
  • 1980s: International metric shift pushed for SI units
    • Problem: 1 mbar = 100 Pa (awkward multiplier)
    • Solution: 1 hectopascal = 100 Pa = 1 mbar (exact equivalence!)
  • 1980s-present: Smooth transition using hPa = mbar equivalence
    • No conversion confusion (same number, new name)
    • Allows decades of data to be "relabeled" without recalculation

Why This Worked

The brilliance: WMO chose hectopascal specifically because:

  1. 100 Pa = 1 hPa (clean, easy power of 10)
  2. 1 hPa = 1 mbar (exact, no confusion)
  3. Sea level pressure stayed ~1,013 hPa (same numbers as before)
  4. All existing meteorology infrastructure could transition seamlessly

Result: Weather services worldwide switched from mbar to hPa with zero data loss.

Common Uses and Applications: inches of mercury vs hectopascals

Explore the typical applications for both Inch of Mercury (imperial/US) and Hectopascal (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 hectopascals

Meteorology: Weather forecasts, atmospheric pressure reporting (worldwide standard). Aviation: Altimeter settings, flight level pressure (ICAO standard). Oceanography: Atmospheric pressure corrections for sea level measurements. Climatology: Historical pressure data, pressure trends. Medical: Altitude acclimatization, pressure chambers, hyperbaric medicine.

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 Hectopascal (hPa)

How do I convert hPa to PSI?

Formula: PSI = hPa × 0.0145

Examples:

  • 1,013 hPa = 14.7 PSI (sea level)
  • 1,000 hPa = 14.5 PSI
  • 900 hPa = 13.05 PSI
  • 800 hPa = 11.6 PSI

hPa to PSI converter →

Is hPa the same as mbar?

Yes, exactly! 1 hPa = 1 mbar

Why two names?:

  • Millibar (mbar): Traditional meteorology unit (1900s-1980s)
  • Hectopascal (hPa): SI-compliant name (1980s-present)
  • Same value, just renamed for SI consistency

Conversion: None needed! They're identical.

Modern usage: Weather services worldwide now use hPa, but many pilots and mariners still say "millibar."

What is normal atmospheric pressure in hPa?

Standard sea level: 1,013.25 hPa (exactly, by definition)

Typical range: 980-1,050 hPa depending on weather

Pressure variations:

  • Fair weather (high): 1,020-1,040 hPa
  • Normal range: 1,000-1,020 hPa
  • Stormy (low): 980-1,000 hPa
  • Hurricane: <980 hPa

Regional/seasonal: Varies ±30 hPa from standard

How does pressure change with altitude?

Rough approximation: Pressure decreases ~12 hPa per 100m near sea level

More accurate (ISA model):

| Altitude | Pressure (hPa) | % of Sea Level | |----------|---------------|----------------| | 0m | 1,013 | 100% | | 500m | 955 | 94% | | 1,000m | 899 | 89% | | 2,000m | 795 | 78% | | 3,000m | 701 | 69% | | 5,000m | 540 | 53% | | 8,848m (Everest) | 313 | 31% |

Formula (approximate): P = 1013 × (1 - altitude/44,300)^5.255

What hPa is considered high or low pressure?

High pressure (anticyclone):

  • Strong high: >1,030 hPa (stable, clear weather)
  • Moderate high: 1,020-1,030 hPa (fair weather)

Normal pressure: 1,005-1,020 hPa

Low pressure (cyclone):

  • Moderate low: 990-1,005 hPa (cloudy, possible rain)
  • Strong low: 970-990 hPa (rain, wind)
  • Very low: <970 hPa (storms, gales)

Extreme low: <920 hPa (major hurricanes/typhoons)

Context: Depends on region and season. 1,000 hPa may be "low" in winter anticyclone, "high" in tropical region.

Conversion Table: Inch of Mercury to Hectopascal

Inch of Mercury (inHg)Hectopascal (hPa)
0.516.932
133.864
1.550.796
267.728
5169.319
10338.639
25846.597
501,693.195
1003,386.389
2508,465.973
50016,931.945
1,00033,863.89

People Also Ask

How do I convert Inch of Mercury to Hectopascal?

To convert Inch of Mercury to Hectopascal, 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.

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

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

Yes! You can easily convert Hectopascal back to Inch of Mercury by using the swap button (⇌) in the calculator above, or by visiting our Hectopascal 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 Hectopascal?

Inch of Mercury and Hectopascal 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