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Atmosphere to Millibar Converter

Convert atmospheres to millibars with our free online pressure converter.

Quick Answer

1 Atmosphere = 1013.25 millibars

Formula: Atmosphere × conversion factor = Millibar

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

Atmosphere to Millibar Calculator

How to Use the Atmosphere to Millibar Calculator:

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

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

Formula:

mbar = atm × 1013.25

Example Calculation:

1 atm = 1013.25 mbar

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 Atmosphere and a Millibar?

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

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

Key relationship: 1 mbar = 1 hPa (exact equivalence)

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

Common Uses and Applications: atmospheres vs millibars

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

Common Uses for 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

When to Use millibars

Aviation: Altimeter settings (pilots say "1015 millibars"). Maritime: Marine weather forecasts, ship barometers. Meteorology: Historical weather data (pre-1980s). Diving: Depth pressure calculations (sometimes).

Additional Unit Information

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.

About Millibar (mbar)

Is mbar the same as hPa?

Yes! 1 mbar = 1 hPa exactly (just different names, same value)

Millibar (mbar):

  • Traditional meteorology unit (1900s-1980s)
  • Still used: Aviation, maritime, older weather services
  • Pilots/mariners: "Set altimeter to 1015 millibars"

Hectopascal (hPa):

  • SI-compliant name (1980s-present)
  • Modern: Weather services worldwide officially use hPa
  • Scientific: Consistent with SI unit system

No conversion needed: 1,013 mbar = 1,013 hPa (identical)

Why two names?: Transition to SI units in 1980s. Chose "hectopascal" because 1 hPa = 1 mbar exactly, making transition seamless. Old term persists in aviation/maritime.

How do I convert mbar to PSI?

Formula: PSI = mbar × 0.0145038

Examples:

  • 1,013 mbar = 14.7 PSI (sea level)
  • 1,000 mbar = 14.5 PSI
  • 900 mbar = 13.05 PSI (storm)
  • 800 mbar = 11.6 PSI
  • 500 mbar = 7.25 PSI (FL180)

mbar to PSI converter →

What is normal atmospheric pressure in mbar?

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

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

Pressure variations:

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

Regional/seasonal: Varies ±30 mbar from standard

Altitude: Decreases ~12 mbar per 100m near sea level

What mbar is considered high or low pressure?

High pressure (anticyclone):

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

Normal pressure: 1,005-1,020 mbar

Low pressure (cyclone):

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

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

Context matters: 1,000 mbar may be "low" in winter high-pressure region, "high" in tropical area.

Why do pilots still say "millibar" instead of "hectopascal"?

Historical training: Aviation training used mbar for decades International: ICAO (aviation authority) still references millibars Brevity: "Millibar" rolls off tongue easier than "hectopascal" Tradition: Aviation conservative about terminology changes Communication: Older pilots, documents use mbar

Modern transition:

  • Official: ICAO now uses hPa in documents
  • Practice: Pilots use both terms interchangeably
  • Altimeter: Settings shown as "1013 hPa" or "1013 mb"

No confusion: Since 1 mbar = 1 hPa exactly, using either term causes no errors.

Maritime similar: Sailors also prefer "millibar" from tradition.

Conversion Table: Atmosphere to Millibar

Atmosphere (atm)Millibar (mbar)
0.5506.625
11,013.25
1.51,519.875
22,026.5
55,066.25
1010,132.5
2525,331.25
5050,662.5
100101,325
250253,312.5
500506,625
1,0001,013,250

People Also Ask

How do I convert Atmosphere to Millibar?

To convert Atmosphere to Millibar, enter the value in Atmosphere 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 Atmosphere to Millibar?

The conversion factor depends on the specific relationship between Atmosphere and Millibar. 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 Millibar back to Atmosphere?

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

Learn more →

What are common uses for Atmosphere and Millibar?

Atmosphere and Millibar 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 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