Free PSI to Inches of Water Converter

PSI to inH₂O Conversion: Essential for Low‑Pressure Measurements

Converting between pounds per square inch (PSI) and inches of water (inH₂O) is a frequent need in technical disciplines such as HVAC, fluid power, and building services. This dedicated PSI to inches of water converter delivers instant and accurate conversions, supporting both directions and a selection of additional pressure units. Whether you are measuring static pressure in ductwork or specifying hydraulic system parameters, this low pressure converter serves as a practical reference.

Understanding the Units

PSI (pounds per square inch)
Represents the force of one pound applied over a one‑square‑inch area. It is the standard unit in the imperial system for hydraulic, pneumatic, and gas pressure applications.

inH₂O (inches of water)
A non‑SI unit that measures the pressure exerted by a column of water at a given height. It is ideally suited for low‑pressure measurements, such as static pressure in air handlers, filter resistance, and gas burner pressure. In the HVAC field, inches of water column (often abbreviated as “water gauge” or “WC”) is the default unit for low‑pressure readings.

Conversion Formula and Underlying Factor

The relationship between PSI and inH₂O is linear and governed by a fixed constant:

$$\text{inH}_2\text{O} = \text{PSI} \times 27.7076$$

To convert inH₂O back to PSI:

$$\text{PSI} = \frac{\text{inH}_2\text{O}}{27.7076}$$

This coefficient (27.7076) is derived from the density of water and standard gravitational acceleration. A useful reciprocal relationship is: 1 inH₂O ≈ 0.036127 PSI.

How to Use the Converter

• Enter any pressure value in the PSI field, and the equivalent in inH₂O appears instantly.
• For the reverse direction, type in inH₂O and read the corresponding PSI result.
• A dropdown menu enables you to select other pressure units (e.g., kPa, bar, atm, or Pa) and get the conversion for that pair as well.

Worked Examples

Example 1: 8 PSI to inH₂O
Using the multiplication factor:

$$\text{inH}_2\text{O} = 8 \times 27.7076 = 221.661$$

Thus, 8 PSI = 221.66 inH₂O (rounded to two decimals).

Example 2: 70 inH₂O to PSI
Dividing by the same factor:

$$\text{PSI} = \frac{70}{27.7076} \approx 2.526$$

Therefore, 70 inH₂O ≈ 2.53 PSI. Both examples are handled instantly by the tool.

Quick Reference Conversion Table

PSI	inH₂O (equivalent)	inH₂O	PSI (equivalent)
1	27.71	10	0.361
2	55.42	50	1.804
5	138.54	100	3.609
10	277.08	200	7.218
20	554.15	500	18.04

(The values are rounded for convenience; the converter uses full precision.)

Significance in HVAC and Industrial Applications

In HVAC, static and dynamic pressures in ducts, fans, and filters are almost always expressed in inches of water column. Because these pressures are often very low (less than 10 inH₂O), using a unit that magnifies small differences — such as inH₂O — is more practical than PSI. On the other hand, compressor discharge, refrigerant lines, and hydraulic cylinders are typically rated in PSI or bar. A seamless PSI to inches of water conversion ensures that technicians and engineers can correctly read dual‑scale instruments and adhere to specifications from different sources.

The converter also serves as a general low pressure converter when other units are needed, bridging the gap between different measurement standards. By eliminating manual calculations, it reduces the risk of unit misinterpretation and helps maintain accuracy in critical systems.