Pressure
inH₂Otoatm
Convert inches of water column (4 °C) (inH₂O) to standard atmospheres (atm).
Factor1 inH₂O = 0.002458316 atm
Converter
inH₂O
Accepts numbers or expressions, e.g. 150 + 14.7
Result
atm
Rendered to 6 significant figures.
Formula
Formula
atm = inH₂O × 0.002458316
Multiply any value in inches of water column (4 °C) by 0.002458316 to obtain the value in standard atmospheres.
Worked example
Convert 400 inH₂O to atm.
- 01Start with 400 inH₂O.
- 02Multiply by the conversion factor: 400 × 0.002458316 = 0.983327 atm.
Result400 inH₂O = 0.983327 atm
Conversion table
| inH₂O | atm |
|---|---|
| 1 | 0.0024583 |
| 2 | 0.0049166 |
| 5 | 0.012292 |
| 10 | 0.024583 |
| 20 | 0.049166 |
| 50 | 0.12292 |
| 100 | 0.24583 |
| 200 | 0.49166 |
| 500 | 1.2292 |
| 1000 | 2.4583 |
Reference values rounded to 5 significant figures for display.
FAQ
What is the conversion factor from inH₂O to atm?
1 inH₂O equals 0.002458316 atm. To convert, multiply the value in inches of water column (4 °C) by 0.002458316.
How do I convert 1 inH₂O to atm?
1 inH₂O = 0.00245832 atm. For any value, multiply by 0.002458316.
How do I convert atm back to inH₂O?
Divide by the same factor — or equivalently, multiply by 406.7825. So 1 atm = 406.782 inH₂O.
When would I need to convert inch of water column (4 °C) to standard atmosphere?
Pressure conversions between inH₂O and atm are common when working with mixed-vendor instrumentation, when piping codes use different units to process datasheets, or when converting field readings into SI for hydraulic calculations.
Is the conversion exact?
The factor shown is precise to at least 7 significant figures. For most process-engineering work this is far better than instrument accuracy. For metrology or trade applications, refer to the relevant national standard (NIST, BIPM, ISO 80000).