Inches of Water to PSI Converter
Convert pressure from inches of water column (inH₂O) to pounds per square inch (PSI) accurately
Conversion Formula
From Inches of Water to PSI:
PSI = inH₂O × 0.0361273
From PSI to Inches of Water:
inH₂O = PSI × 27.6799
The conversion factor is derived from the pressure exerted by a column of water at 4°C (39.2°F) with standard gravity (9.80665 m/s²).
Conversion Examples
Example 1: Converting 10 inH₂O to PSI
Given: 10 inches of water
Formula: PSI = inH₂O × 0.0361273
Calculation: PSI = 10 × 0.0361273 = 0.361273
Result: 10 inH₂O = 0.361273 PSI
Example 2: Converting 50 inH₂O to PSI
Given: 50 inches of water
Formula: PSI = inH₂O × 0.0361273
Calculation: PSI = 50 × 0.0361273 = 1.806365
Result: 50 inH₂O = 1.806365 PSI
Example 3: Converting 2 PSI to inH₂O
Given: 2 pounds per square inch
Formula: inH₂O = PSI × 27.6799
Calculation: inH₂O = 2 × 27.6799 = 55.3598
Result: 2 PSI = 55.36 inH₂O
Detailed Conversion Table
| Inches of Water (inH₂O) | PSI | Rounded PSI |
|---|---|---|
| 1 | 0.036127 | 0.036 |
| 2 | 0.072255 | 0.072 |
| 5 | 0.180636 | 0.181 |
| 10 | 0.361273 | 0.361 |
| 15 | 0.541909 | 0.542 |
| 20 | 0.722546 | 0.723 |
| 25 | 0.903182 | 0.903 |
| 30 | 1.083819 | 1.084 |
| 40 | 1.445091 | 1.445 |
| 50 | 1.806365 | 1.806 |
| 60 | 2.167637 | 2.168 |
| 75 | 2.709547 | 2.710 |
| 100 | 3.612730 | 3.613 |
| 125 | 4.515912 | 4.516 |
| 150 | 5.419095 | 5.419 |
| 200 | 7.225460 | 7.225 |
| 250 | 9.031825 | 9.032 |
| 300 | 10.838190 | 10.838 |
| 500 | 18.063650 | 18.064 |
| 1000 | 36.127300 | 36.127 |
PSI to Inches of Water Table
| PSI | Inches of Water (inH₂O) | Rounded inH₂O |
|---|---|---|
| 0.1 | 2.768 | 2.77 |
| 0.25 | 6.920 | 6.92 |
| 0.5 | 13.840 | 13.84 |
| 0.75 | 20.760 | 20.76 |
| 1 | 27.680 | 27.68 |
| 1.5 | 41.520 | 41.52 |
| 2 | 55.360 | 55.36 |
| 2.5 | 69.200 | 69.20 |
| 3 | 83.040 | 83.04 |
| 4 | 110.720 | 110.72 |
| 5 | 138.400 | 138.40 |
| 7.5 | 207.599 | 207.60 |
| 10 | 276.799 | 276.80 |
| 15 | 415.199 | 415.20 |
| 20 | 553.598 | 553.60 |
Popular Pressure Conversions
Inches of water and PSI can be converted to various other pressure units:
About Inches of Water (inH₂O)
Inches of water column (inH₂O or inch water gauge) is a unit of pressure measurement representing the pressure exerted by a column of water at a specific height. This unit is commonly used in:
- HVAC systems for measuring air pressure differences
- Gas pressure measurements in residential and commercial applications
- Ventilation system design and testing
- Medical equipment pressure monitoring
- Industrial process control
The measurement is typically referenced at 4°C (39.2°F), where water has its maximum density. One inch of water column equals approximately 0.03613 PSI or 249.089 pascals.
About Pounds Per Square Inch (PSI)
Pounds per square inch (PSI) is a widely used pressure unit in English-speaking countries, particularly in the United States. It represents the force of one pound applied to an area of one square inch. PSI is the standard unit for:
- Tire pressure measurements
- Hydraulic and pneumatic systems
- Water pressure in plumbing systems
- Compressed air applications
- Pressure vessel specifications
- Industrial equipment ratings
One PSI equals 6,894.76 pascals or approximately 27.68 inches of water column. PSI is part of the imperial measurement system and remains prevalent in many engineering and industrial applications.
Applications in Real-World Scenarios
HVAC Systems
In heating, ventilation, and air conditioning systems, pressure measurements in inches of water are critical for balancing airflow and system performance. Static pressure readings typically range from 0.1 to 3 inH₂O (0.0036 to 0.108 PSI), helping technicians optimize fan speeds and ductwork design.
Gas Appliances
Natural gas systems often operate at pressures measured in inches of water column. Typical residential gas pressure is around 7 inH₂O (0.25 PSI), while commercial applications may require higher pressures. Accurate conversion to PSI helps in regulator selection and safety valve sizing.
Medical Equipment
Respiratory therapy equipment, ventilators, and CPAP machines measure airway pressure in centimeters or inches of water. Converting these values to PSI aids in comparing specifications across different measurement systems and equipment types.
Industrial Process Control
Many industrial processes monitor differential pressure across filters, fans, and blowers using inches of water. Converting to PSI allows integration with equipment rated in standard pressure units and facilitates system design calculations.
Frequently Asked Questions
How many PSI is 1 inch of water?
One inch of water column (inH₂O) equals approximately 0.036127 PSI. This conversion is based on water at 4°C (39.2°F) under standard gravity conditions (9.80665 m/s²).
How many inches of water equal 1 PSI?
One PSI equals approximately 27.68 inches of water column. This means that a pressure of 1 pound per square inch is equivalent to the pressure exerted by a 27.68-inch tall column of water.
Why is water temperature important in this conversion?
Water density changes with temperature, which affects the pressure exerted by a water column of specific height. The standard reference is 4°C (39.2°F), where water reaches its maximum density of approximately 1000 kg/m³. Using this standard allows for consistent and accurate conversions.
What industries commonly use inches of water as a pressure unit?
Inches of water is commonly used in HVAC, natural gas distribution, medical equipment (ventilators and CPAP machines), industrial ventilation, clean room design, and pneumatic conveying systems. The unit is particularly useful for measuring low-pressure differentials.
Can I use this conversion for other liquids besides water?
No, this conversion is specific to water at 4°C. Different liquids have different densities, which would result in different pressure values for the same column height. For other liquids, you would need to use density-adjusted conversion factors.
How accurate is the conversion factor 0.036127?
The conversion factor 0.0361273 is highly accurate for most practical applications. It’s derived from fundamental physical constants and standard conditions. For precision engineering or scientific applications, additional decimal places may be used (0.03612729499), but the shortened version is sufficient for typical industrial and commercial uses.
What is the difference between inH₂O and inches water gauge (iwg)?
InH₂O (inches of water) and iwg (inches water gauge) refer to the same measurement unit. Both represent gauge pressure measured as the height of a water column. The terms are used interchangeably in most applications.
How does atmospheric pressure affect these measurements?
Both inH₂O and PSI can be expressed as either absolute pressure or gauge pressure. Gauge pressure measures pressure relative to atmospheric pressure, while absolute pressure includes atmospheric pressure. In most HVAC and industrial applications, gauge pressure is used, meaning the readings are relative to ambient atmospheric conditions.
References
- National Institute of Standards and Technology (NIST). (2019). “Guide for the Use of the International System of Units (SI).” NIST Special Publication 811.
- ASHRAE. (2021). “ASHRAE Handbook – Fundamentals.” American Society of Heating, Refrigerating and Air-Conditioning Engineers.
- International Organization for Standardization. (2020). “ISO 80000-4:2019 – Quantities and units – Part 4: Mechanics.” ISO Standards.
- Bureau International des Poids et Mesures (BIPM). (2019). “The International System of Units (SI).” 9th edition.
- American Gas Association. (2018). “Gas Engineers Handbook.” Industrial Press.