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Technical Atmosphere to Inch of Water Column Converter

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

Quick Answer

1 Technical Atmosphere = 393.70079 inches of water column

Formula: Technical Atmosphere × conversion factor = Inch of Water Column

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

Technical Atmosphere to Inch of Water Column Calculator

How to Use the Technical Atmosphere to Inch of Water Column Calculator:

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

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

Formula:

inH₂O = at × 393.701

Example Calculation:

1 at = 393.70079 inH₂O

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.

Need to convert to other pressure units?

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📋 Unit Symbols

Copy at & inH₂O symbols

What is a Technical Atmosphere and a Inch of Water Column?

1 at = 1 kgf/cm² = 98,066.5 Pa = 98.07 kPa = 0.9807 bar = 0.968 atm = 14.223 PSI = 735.6 mmHg

Symbol: at (from German "technische Atmosphäre")

Also written as: kgf/cm², kg/cm², technical atmosphere, metric atmosphere (not standard atmosphere!)

Physical meaning: Pressure exerted by 1 kilogram-force over 1 square centimeter

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

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

Common Uses and Applications: technical atmospheres vs inches of water column

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

Common Uses for technical atmospheres

Historical: European engineering (Germany, Austria, Switzerland) pre-1980s. Current: Some Asian countries (China, Russia, Japan) still use occasionally. Older Equipment: Pressure gauges, hydraulic systems from mid-1900s. Legacy Specs: Old engineering drawings, technical manuals.

When to Use 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.

Additional Unit Information

About Technical Atmosphere (at)

What is the difference between "at" and "atm"?

Different units! (Common source of confusion)

at (technical atmosphere):

  • 1 at = 1 kgf/cm² = 98,066.5 Pa
  • Engineering unit based on kilogram-force
  • Symbol: at
  • Historical European engineering

atm (standard atmosphere):

  • 1 atm = 101,325 Pa (exactly, by definition)
  • Based on sea-level atmospheric pressure
  • Symbol: atm
  • Scientific/meteorological standard

Relationship: 1 atm = 1.033 at (about 3% higher)

Why confusion?: Names sound similar, values close (both ≈ atmospheric pressure)

Technical Atmosphere to Atmosphere converter →

How do I convert at to bar?

Formula: bar = at × 0.980665

Quick approximation: 1 at ≈ 1 bar (1.9% difference)

Exact conversions:

  • 1 at = 0.981 bar
  • 2 at = 1.961 bar
  • 5 at = 4.903 bar
  • 10 at = 9.807 bar
  • 100 at = 98.07 bar

Inverse: 1 bar = 1.0197 at

Why so close?: Bar defined (originally) to be close to atmospheric pressure, similar motivation as technical atmosphere

at to Bar converter →

How do I convert at to PSI?

Formula: PSI = at × 14.2233

Examples:

  • 1 at = 14.22 PSI
  • 2 at = 28.45 PSI
  • 5 at = 71.12 PSI (typical air compressor)
  • 10 at = 142.23 PSI
  • 100 at = 1,422.33 PSI (high pressure)

Inverse: 1 PSI = 0.0703 at

Memory aid: 1 at ≈ 14 PSI

at to PSI converter →

How do I convert at to kPa or MPa?

Formula: kPa = at × 98.0665

Examples:

  • 1 at = 98.07 kPa ≈ 0.1 MPa
  • 5 at = 490.3 kPa ≈ 0.5 MPa
  • 10 at = 980.7 kPa ≈ 1 MPa
  • 50 at = 4,903 kPa ≈ 5 MPa
  • 100 at = 9,807 kPa ≈ 10 MPa

Quick rule: Multiply by ~100 to get kPa, divide by ~10 to get MPa

at to kPa converter → at to MPa converter →

Why is this unit not used anymore?

SI adoption (1970s-1980s): Most countries transitioned to SI units (Pa, kPa, MPa, bar)

Problems with technical atmosphere:

  • Not SI-compliant: Based on kilogram-force (gravitational unit)
  • Ambiguity: "kg" is mass, not force (kgf needed for clarity)
  • Gravity dependence: Assumes standard gravity (9.80665 m/s²)
  • Confusion: Easy to confuse with standard atmosphere (atm)

Modern replacements:

  • Bar: 1 at ≈ 1 bar (easy conversion)
  • kPa: 1 at ≈ 100 kPa
  • MPa: For high pressures (1 at = 0.1 MPa)

Still seen in:

  • Older European equipment specifications
  • Chinese industrial standards (some applications)
  • Russian/former Soviet engineering documents
  • Japanese industrial equipment (occasionally)
  • Legacy pressure gauges and instruments

For new designs: Use bar, kPa, or MPa instead of at

Historical importance: Was convenient unit when bar not yet standardized, and provided easy mental approximation to atmospheric pressure.

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)

Conversion Table: Technical Atmosphere to Inch of Water Column

Technical Atmosphere (at)Inch of Water Column (inH₂O)
0.5196.85
1393.701
1.5590.551
2787.402
51,968.504
103,937.008
259,842.52
5019,685.04
10039,370.079
25098,425.198
500196,850.395
1,000393,700.79

People Also Ask

How do I convert Technical Atmosphere to Inch of Water Column?

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

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

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

Learn more →

What are common uses for Technical Atmosphere and Inch of Water Column?

Technical Atmosphere and Inch of Water Column 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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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