PSI to Inches of Water Calculator: Convert Pounds per Square Inch to In H2O
Convert pounds per square inch (PSI) to inches of water (In H2O) with ease using our calculator. This tool provides accurate conversion based on standard conditions, helping professionals across industries where water column pressure is critical.
Understanding PSI to Inches of Water Conversion
Converting PSI (pounds per square inch) to inches of water column (In H2O) is essential in fields such as HVAC, environmental monitoring, fluid dynamics, and low-pressure systems. While PSI is a standard imperial unit for pressure, inches of water are commonly used for low-pressure measurements due to their fine resolution and relevance to fluid-based systems.
Conversion Factor
Under standard conditions (temperature 4°C and gravitational acceleration 9.80665 m/s²), 1 PSI is equivalent to approximately 27.7076 inches of water.
| Unit | Symbol | Equivalent |
|---|---|---|
| Pounds per square inch | PSI | 1 PSI = 27.7076 In H2O |
| Inches of water | In H2O | 1 In H2O = 0.03613 PSI |
Formula
In H2O = PSI × 27.7076
This formula assumes standard temperature and atmospheric conditions. For specialized systems (e.g., high-temperature steam or compressed gases), corrections may apply.
Why Convert PSI to Inches of Water?
PSI is often too coarse a measurement for sensitive instruments or low-pressure systems. In contrast, inches of water provide a more granular scale, making it easier to measure and regulate subtle pressure changes in ventilation ducts, liquid levels, or gas flows.
Examples of Practical Use
- HVAC Systems: Duct static pressure is usually measured in In H2O. For example, 0.5 PSI is equivalent to ~13.85 inches of water — a typical range for system balancing.
- Barometric Pressure: Atmospheric pressure is ~407 inches of water (~14.7 PSI).
- Bubblers & Tank Level Monitoring: Head pressure of a liquid column is often expressed in inches of water.
Limitations and Considerations
Although PSI and In H2O are both pressure units, they differ in application. PSI is favored for high-pressure systems like hydraulics, while In H2O is ideal for measuring low-pressure variations. Also, temperature and fluid density affect actual conversion in precise scientific or engineering applications.
Frequently Asked Questions
Is the conversion from PSI to In H2O temperature dependent?
Yes. The standard factor (1 PSI = 27.7076 In H2O) assumes 4°C water and standard gravity. Higher temperatures can slightly decrease water density, changing the conversion rate.
Can I use this calculator for HVAC system design?
Absolutely. Most duct pressure measurements are taken in inches of water. If your instrument reads PSI, this calculator helps ensure compliance with manufacturer pressure guidelines.
What is the smallest measurable pressure using In H2O?
Modern sensors can resolve changes as small as 0.01 In H2O, making the unit highly suitable for differential pressure sensing in clean rooms, lab environments, and medical equipment.
Is PSI still relevant in low-pressure systems?
While PSI can technically be used for low-pressure systems, In H2O is more precise and conventional. PSI remains dominant in mechanical and structural applications where higher pressures are common.