Pressure
atmtoinH₂O
Convert standard atmospheres (atm) to inches of water column (4 °C) (inH₂O).
Factor1 atm = 406.7825 inH₂O
Converter
atm
Accepts numbers or expressions, e.g. 150 + 14.7
Result
inH₂O
Rendered to 6 significant figures.
Formula
Formula
inH₂O = atm × 406.7825
Multiply any value in standard atmospheres by 406.7825 to obtain the value in inches of water column (4 °C).
Worked example
Convert 1 atm to inH₂O.
- 01Start with 1 atm.
- 02Multiply by the conversion factor: 1 × 406.7825 = 406.782 inH₂O.
Result1 atm = 406.782 inH₂O
Conversion table
| atm | inH₂O |
|---|---|
| 1 | 406.78 |
| 2 | 813.56 |
| 5 | 2033.9 |
| 10 | 4067.8 |
| 20 | 8135.6 |
| 50 | 20339 |
| 100 | 40678 |
| 200 | 81356 |
| 500 | 2.0339e+5 |
| 1000 | 4.0678e+5 |
Reference values rounded to 5 significant figures for display.
FAQ
What is the conversion factor from atm to inH₂O?
1 atm equals 406.7825 inH₂O. To convert, multiply the value in standard atmospheres by 406.7825.
How do I convert 1 atm to inH₂O?
1 atm = 406.782 inH₂O. For any value, multiply by 406.7825.
How do I convert inH₂O back to atm?
Divide by the same factor — or equivalently, multiply by 0.002458316. So 1 inH₂O = 0.00245832 atm.
When would I need to convert standard atmosphere to inch of water column (4 °C)?
Pressure conversions between atm and inH₂O 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).