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Inch of Water Column to Hectopascal Converter

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

Quick Answer

1 Inch of Water Column = 2.490889 hectopascals

Formula: Inch of Water Column × 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 Water Column to Hectopascal Calculator

How to Use the Inch of Water Column to Hectopascal Calculator:

  1. Enter the value you want to convert in the 'From' field (Inch of Water Column).
  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 Water Column to Hectopascal: Step-by-Step Guide

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

Formula:

hPa = inH₂O × 2.49089

Example Calculation:

1 inH₂O = 2.490889 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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📋 Unit Symbols

Copy inH₂O & hPa symbols

What is a Inch of Water Column and a Hectopascal?

1 inH₂O = 249.1 Pa = 2.491 mbar = 0.2491 hPa = 0.0361 PSI = 0.00249 bar = 0.0736 inHg = 1.868 mmH₂O

Also written as: in wc (inches water column), "H₂O, inAq

Physical meaning: Pressure exerted by 1-inch column of water at standard conditions

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 Water Column 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 Water Column 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 water column vs hectopascals

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

Common Uses for inches of water column

HVAC: Duct pressure, fan static pressure, filter pressure drop. Building Systems: Room pressurization, clean room differentials. Industrial: Low-pressure gas systems, ventilation. Testing: Air tightness testing, pressure differential measurements.

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 Water Column (inH₂O)

How do I convert inH₂O to PSI?

Formula: PSI = inH₂O × 0.0361273

Examples:

  • 1 inH₂O = 0.036 PSI
  • 2 inH₂O = 0.072 PSI (typical duct)
  • 5 inH₂O = 0.181 PSI
  • 10 inH₂O = 0.361 PSI (gas manifold)
  • 27.7 inH₂O = 1 PSI

inH₂O to PSI converter →

How do I convert inH₂O to Pascals or mbar?

Formula:

  • Pa = inH₂O × 249.1
  • mbar = inH₂O × 2.491

Examples:

  • 1 inH₂O = 249.1 Pa = 2.49 mbar
  • 0.5 inH₂O = 124.5 Pa = 1.25 mbar (residential duct)
  • 2 inH₂O = 498 Pa = 4.98 mbar (commercial duct)
  • 4 inH₂O = 996 Pa = 9.96 mbar (high static)

inH₂O to Pascal converter →

What is normal static pressure in HVAC?

Residential systems:

  • Total external static pressure: 0.4-0.8 inH₂O (target)
  • Supply side: 0.2-0.5 inH₂O
  • Return side: 0.1-0.3 inH₂O

High static pressure problems (>1.0 inH₂O total):

  • Reduced airflow
  • Higher energy costs
  • Shortened equipment life
  • Possible compressor damage

Low static pressure (<0.3 inH₂O):

  • May indicate oversized ductwork
  • Can cause noise issues

Commercial/Industrial: 1-4 inH₂O typical (design dependent)

When should I replace an HVAC filter?

Pressure drop method (most accurate):

  • MERV 8: Replace at 0.5 inH₂O
  • MERV 11-13: Replace at 0.7-1.0 inH₂O
  • HEPA: Replace at 2-3 inH₂O

Without gauge:

  • Monthly inspection
  • Every 1-3 months residential
  • More often if pets, allergies, construction

Measure with: Magnehelic gauge or manometer across filter

Why use inH₂O instead of PSI for HVAC?

Appropriate scale: HVAC pressures very low (0.1-2 inH₂O = 0.004-0.072 PSI) Historical: Water manometers traditional measurement tool Precision: Easier to read 0.5 inH₂O than 0.018 PSI Industry standard: ASHRAE, building codes specify inH₂O Instruments: Magnehelic gauges, manometers calibrated in inH₂O

Conversion: ~28 inH₂O = 1 PSI (HVAC uses tiny fraction of PSI)

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 Water Column to Hectopascal

Inch of Water Column (inH₂O)Hectopascal (hPa)
0.51.245
12.491
1.53.736
24.982
512.454
1024.909
2562.272
50124.545
100249.089
250622.722
5001,245.445
1,0002,490.889

People Also Ask

How do I convert Inch of Water Column to Hectopascal?

To convert Inch of Water Column to Hectopascal, enter the value in Inch of Water Column 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 Water Column to Hectopascal?

The conversion factor depends on the specific relationship between Inch of Water Column 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 Water Column?

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

Learn more →

What are common uses for Inch of Water Column and Hectopascal?

Inch of Water Column 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