Inches WG to Pa Converter
Convert pressure readings between imperial and metric HVAC specifications for fan data, filters and air-handling equipment. Keep reference conditions consistent when comparing values across technical documents.
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Inches WG to Pa formula
Pa = in. w.g. × 249.08891
in. w.g. = Pa ÷ 249.08891
The factor is 249.08891 Pa for each 1 in. w.g.. Going the other way, 1 Pa is 0.0040146308 in. w.g..
Inches WG to Pa reference table
| in. w.g. | Pa |
|---|---|
| 0.05 | 12.4544 |
| 0.1 | 24.9089 |
| 0.25 | 62.2722 |
| 0.5 | 124.544 |
| 0.75 | 186.817 |
| 1 | 249.089 |
| 1.5 | 373.633 |
| 2 | 498.178 |
| 4 | 996.356 |
| 6 | 1,494.53 |
Where this conversion is used
Fan static pressure, filter pressure drop, duct friction rates and room pressure differentials are given in inches of water gauge in US data and in pascals in metric data. On projects in India and the Gulf you often see both on the same job. Use this conversion for fan selection, for the external static pressure of AHUs and for cleanroom or stairwell pressurisation values. This page uses 249.089 Pa per in. w.g., the conventional value for water at 4 °C. Some references use about 248.84 Pa, which is based on water at 60 °F.
Worked example
An AHU needs 2.5 in. w.g. of external static pressure and the fan curves in the catalogue are plotted in Pa.
2.5 in. w.g. × 249.08891 = 622.722 Pa
Select the fan at about 622.7 Pa.
Common mistakes
- Mixing inches of water with inches of mercury. An inch of mercury is a much larger pressure, more than 13 times an inch of water.
- Mixing static, velocity and total pressure. Convert like with like and state which one the figure is.
- Converting a friction rate without its length basis. A rate in in. w.g. per 100 ft needs the length converted as well before it can be compared with Pa/m.
Related HVAC Tools and Business Resources
Frequently asked questions
How many pascals does one inch of water gauge represent in HVAC readings?
One inch of water gauge is approximately 249.09 Pa under the conventional inH₂O factor. For an Inches WG to Pa conversion, multiply the reading by 249.0889. If the specification uses water at 60°F, the factor is 248.84 Pa per inch. Keep the reference condition consistent when comparing equipment data.
How can you convert Pa readings to inches of water column while keeping units consistent?
Divide the pressure in pascals by the conversion factor specified for the project. Use 249.0889 for the conventional factor or 248.84 when the reference is water at 60°F. For Pa to inches WG, confirm the reference before comparing results with equipment specifications.
Are in. w.g., in. w.c. and inH₂O interchangeable in HVAC specifications?
These abbreviations commonly represent pressure measured in inches of water column, but the reference convention should still be checked. For an in wc to pascal conversion, use the factor specified by the equipment documentation or project standard. For readings in millimetres of water, a mmH2O to pascal converter requires the corresponding millimetre-based factor.
Why do some pressure converters show 249.09 Pa while others show 248.84 Pa for one inch of water?
The difference comes from the reference definition used for the conversion. NIST lists 1 inH₂O as approximately 249.0889 Pa, while ASHRAE specifies 248.84 Pa for an inch of water at 60°F. An in wg to pa converter should use the convention appropriate to the specification being checked. Always confirm the reference before comparing results.
When is an HVAC pressure unit converter useful for project documents?
An HVAC pressure unit converter helps standardize pressure values across fan schedules, filter specifications, equipment submittals and test reports. A psi to kPa pressure conversion uses a different conversion factor from water-column pressure. Check the pressure type and units before comparing readings from different documents.
What does fan static pressure conversion tell you about HVAC equipment?
Fan static pressure conversion expresses the same pressure in a different unit; it does not confirm whether a fan is correctly selected. Check the manufacturer's fan curve against the required airflow and system resistance. A converted pressure value alone cannot establish fan performance.
What should an external static pressure calculator consider?
An external static pressure calculator should use the defined measurement points, required airflow and applicable equipment rating limits. Confirm which external components are included in the rating, such as filters or coils, before interpreting the result. Consistent measurement boundaries are essential for a meaningful comparison.
How does duct friction rate metric conversion affect HVAC duct sizing?
Duct friction rate metric conversion expresses pressure loss per unit of duct length in consistent units, such as inches of water gauge per 100 feet and pascals per metre. Convert both pressure and length using a consistent reference convention. An HVAC duct sizing calculator requires additional design inputs, including airflow and duct dimensions, so converting friction rate alone does not determine duct size.