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Hectopascal to Millimeter of Mercury Converter

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

Quick Answer

1 Hectopascal = 0.750062 millimeters of mercury

Formula: Hectopascal × conversion factor = Millimeter 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

Hectopascal to Millimeter of Mercury Calculator

How to Use the Hectopascal to Millimeter of Mercury Calculator:

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

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

Formula:

mmHg = hPa × 0.750062

Example Calculation:

1 hPa = 0.750062 mmHg

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 Hectopascal and a Millimeter of Mercury?

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

The millimeter of mercury (symbol: mmHg) is a manometric unit of pressure.

The Physical Definition: It is defined as the pressure exerted at the base of a column of mercury exactly 1 millimeter high at a temperature of 0°C (32°F) under standard gravity.

Relation to SI Units: 1 mmHg ≈ 133.322387415 Pascals.

mmHg vs. Torr: While the terms are often used interchangeably, there is a tiny technical difference:

  • Torr is defined as exactly 1/760 of a standard atmosphere.
  • mmHg is based on the physical properties of mercury.
  • The difference is roughly 0.000015%. For all medical, engineering, and everyday purposes, 1 mmHg = 1 Torr.

Key standard relationships:

  • 1 mmHg = 1 Torr
  • 760 mmHg = 1 standard atmosphere (atm)
  • 1 mmHg ≈ 1.333 millibars (mbar)
  • 1 mmHg ≈ 0.0193 PSI

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

History of the Hectopascal and Millimeter of Mercury

: 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.

: Torricelli and the Liquid Silver

The mmHg is one of the oldest measurement units still in daily use.

1. The Invention of the Barometer (1643)

Before 1643, people believed suction "pulled" water up pipes. Evangelista Torricelli proved this was wrong. He filled a tube with mercury (which is much heavier than water) and saw it settle at 76 cm. He realized it wasn't a pull, but a "push" from the weight of the invisible atmosphere.

2. Why Mercury?

Mercury was chosen because it is the only metal that is liquid at room temperature and is extremely dense (13.6 times heavier than water). If Torricelli had used water, his barometer would have needed to be over 34 feet (10 meters) tall to measure the same atmospheric weight!

3. The Move to Absolute Values

In the mid-20th century, scientists realized that a "millimeter" of mercury actually weighed more in some places than others (due to gravity differences). To fix this, the Torr was created as a fixed mathematical fraction of an atmosphere, while the mmHg remained as the descriptive name for the liquid measurement.

Common Uses and Applications: hectopascals vs millimeters of mercury

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

Common Uses for 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.

When to Use millimeters of mercury

Additional Unit Information

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.

About Millimeter of Mercury (mmHg)

What is normal blood pressure in mmHg?

120/80 mmHg is considered normal adult blood pressure

120 mmHg (systolic):

  • Pressure in arteries when heart beats/contracts
  • Upper number in blood pressure reading

80 mmHg (diastolic):

  • Pressure in arteries when heart rests between beats
  • Lower number in blood pressure reading

Blood pressure categories (American Heart Association):

  • Normal: <120/<80 mmHg
  • Elevated: 120-129/<80 mmHg
  • Stage 1 Hypertension: 130-139/80-89 mmHg
  • Stage 2 Hypertension: ≥140/90 mmHg
  • Hypertensive Crisis: >180/120 mmHg (seek emergency care)

How do I convert mmHg to PSI?

Formula: PSI = mmHg × 0.0193368

Examples:

  • 120 mmHg = 2.32 PSI (systolic blood pressure)
  • 80 mmHg = 1.55 PSI (diastolic blood pressure)
  • 760 mmHg = 14.7 PSI (atmospheric pressure)
  • 100 mmHg = 1.93 PSI
  • 10 mmHg = 0.19 PSI

mmHg to PSI converter →

Why is blood pressure measured in mmHg?

Historical: Early sphygmomanometers (blood pressure cuffs) used mercury columns Standardization: Established globally since early 1900s Accuracy: Mercury barometers very accurate and reliable Consistency: Changing units would cause confusion in medical field Universal: Understood by doctors, nurses, patients worldwide

Modern devices: Digital monitors still display mmHg for consistency, even though they don't use actual mercury.

Why not change?:

  • Medical literature, guidelines all use mmHg
  • Training and education based on mmHg
  • Patient familiarity (everyone knows "120 over 80")
  • Risk of errors during transition period

What is the difference between mmHg and Torr?

Virtually identical: 1 mmHg ≈ 1 Torr (difference < 0.000015%)

mmHg (Millimeter of Mercury):

  • Based on mercury density at 0°C, standard gravity
  • Slightly temperature/gravity dependent
  • Preferred in medicine (blood pressure)

Torr:

  • Defined as exactly 1/760 atmosphere
  • Independent of mercury properties
  • Preferred in vacuum technology, physics

Practical usage: Treat them as equal—difference is negligible for all practical purposes.

Conversion: 1 mmHg = 1.000000142 Torr (effectively 1:1)

mmHg to Torr converter →

How many mmHg is 1 atmosphere?

1 atm = 760 mmHg (exactly, by definition)

This is the height of mercury column supported by atmospheric pressure at sea level.

Examples:

  • 0.5 atm = 380 mmHg
  • 1 atm = 760 mmHg (sea level)
  • 2 atm = 1,520 mmHg (diving 10m deep)
  • 3 atm = 2,280 mmHg (diving 20m deep)

Altitude effect:

  • Sea level: 760 mmHg
  • Denver (1,609m): ~630 mmHg
  • La Paz, Bolivia (3,640m): ~480 mmHg
  • Mount Everest (8,848m): ~253 mmHg

Atmosphere to mmHg converter →

Will medicine switch from mmHg to kPa?

Slow transition, likely decades away (if ever)

Current status:

  • Still dominant: Most medical equipment worldwide uses mmHg
  • Some countries transitioning: Australia, Canada partially adopted kPa
  • Dual display: Modern monitors often show both mmHg and kPa
  • Guidelines: International medical guidelines still primarily use mmHg

Challenges to switching:

  • Familiarity: "120/80" universally understood
  • Education: Medical training globally uses mmHg
  • Communication: Doctor-patient communication simpler with mmHg
  • Standards: Hypertension thresholds defined in mmHg
  • Risk: Potential for medication errors during transition

Conversion: 120/80 mmHg = 16.0/10.7 kPa (less intuitive)

Prediction: mmHg likely to persist in medicine for foreseeable future despite SI adoption elsewhere.

Conversion Table: Hectopascal to Millimeter of Mercury

Hectopascal (hPa)Millimeter of Mercury (mmHg)
0.50.375
10.75
1.51.125
21.5
53.75
107.501
2518.752
5037.503
10075.006
250187.515
500375.031
1,000750.062

People Also Ask

How do I convert Hectopascal to Millimeter of Mercury?

To convert Hectopascal to Millimeter of Mercury, enter the value in Hectopascal 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 Hectopascal to Millimeter of Mercury?

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

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

Learn more →

What are common uses for Hectopascal and Millimeter of Mercury?

Hectopascal and Millimeter 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 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 TorrTechnical Atmosphere to Millimeter of Mercury

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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