Convert psi to inches of water with the exact factor for your selected reference standard so small table-to-table differences make sense.
Table of contents
How to use our PSI to Inches of Water Converter
- Enter your value in Pressure (psi). You can use a negative number if you are working with a signed pressure difference.
- Choose an Inches of water reference that matches your source, table, manual, or instrument.
- Pick Decimal places to control how many digits appear in the converted result.
- Click Calculate to see Inches of water, the Factor used, the Formula used, and a short Reference note.
- Sanity-check the answer by dividing Inches of water by Pressure (psi); it should match the shown Factor used for the selected reference.
Definitions
psi: Pounds per square inch, a pressure unit based on force spread over one square inch.
inH2O: Inches of water, also called inches of water column or water column, a small-pressure unit based on the pressure from a column of water.
Inches of water reference: The standard used to define the water-column pressure. Different references can change the factor slightly.
Factor used: The multiplier in inH2O per psi. Multiply Pressure (psi) by this factor to get Inches of water.
Decimal places: How many digits show after the decimal point in the displayed result. This changes display precision, not the underlying conversion rule.
Common mistakes and quick fixes
Mistake: Leaving Pressure (psi) blank or typing text that is not a number.
Fix: Enter a finite numeric value in Pressure (psi) , such as 1, 10, or -0.5.
Mistake: Comparing your Inches of water result to another site without checking Inches of water reference .
Fix: Match the same Inches of water reference first, then compare the numbers.
Mistake: Assuming Factor used is always exactly the same on every table.
Fix: Read Reference note and use the displayed Factor used for your chosen basis.
Mistake: Expecting a negative Pressure (psi) to turn into a positive Inches of water value.
Fix: Keep the sign consistent; a negative Pressure (psi) gives a negative Inches of water result.
Mistake: Reading rounded output as if it were the exact stored value.
Fix: Increase Decimal places when you need a closer displayed match for calculations or table checks.
Limitations & Key Assumptions / Boundary Conditions
- The result depends on the selected Inches of water reference. Different standards use slightly different factors, so small mismatches across sites can be normal.
- This converter is for unit conversion only. It does not correct for instrument calibration, local fluid density, elevation, or system losses.
- Negative values in Pressure (psi) stay negative in Inches of water. That is useful for signed pressure difference cases, but it may not match every gauge's display convention.
- Decimal places changes only how the answer is shown on screen. Rounded display values can differ slightly from full-precision internal values.
- If a manual or device uses a special house standard for water column, its number can differ from all three reference choices shown here.
Methodology
Conversion rule
The calculator converts psi to inches of water by multiplying the entered pressure by the selected reference factor.
inH2O = psi * k
In this formula, k is the selected conversion factor in inH2O per psi.
Reference factors used
Three inch-of-water bases are supported so you can match common standards and explain small differences between tables.
4 C basis: k = 27.6806714 inH2O per psi
60 F basis: k = 27.6808939 inH2O per psi
NIST gas-flow table basis: k = 27.67990 inH2O per psi
These small differences happen because inches of water depends on the reference definition used for the water column.
Bridge from pascals
The factors can also be written from the standard pressure value for 1 psi and the chosen pascal value for 1 inch of water.
k = 6894.757 / Pa_per_inH2O
6894.757 Pa = 1 psi
For example, using the 4 C basis:
k = 6894.757 / 249.082 = 27.6806714
Worked example
If Pressure (psi) is 10 and the selected Inches of water reference is 60 F, then:
inH2O = 10 * 27.6808939 = 276.808939
With Decimal places set to 4, the displayed Inches of water is 276.8089.
Assumptions and limits
This method assumes the chosen reference factor is the one you want to match. It is a direct unit conversion, so it does not model sensor error, fluid contamination, non-water liquids, or instrument-specific rounding. Negative psi values are allowed and the sign is preserved in the converted result.