Direct conversion
Convert inch of water [inH2O] to millimeter of water [mmH2O] instantly with formula, examples, chart, and FAQs.
1 inch of water [inH2O] = 25.4 millimeter of water [mmH2O]
1 inch of water [inH2O] = 25.4 millimeter of water [mmH2O]
Example: 1 inch of water [inH2O] equals 25.4 millimeter of water [mmH2O].
Pressure conversions use pascal as the reference unit and include common engineering, weather, tire, and laboratory pressure units.
Displayed results are rounded for readability. The calculator keeps enough precision for everyday use and switches to scientific notation for very large or very small values. Last reviewed: 2026-08-14.
The inch of water (inH2O) is a pressure unit used to express measurements in this converter.
HistoryThis unit is included because it appears in practical measurement systems, technical references, product specifications, or everyday conversion needs.
Current useUse inch of water when comparing pressure values, checking specifications, converting between systems, or preparing quick estimates.
The millimeter of water (mmH2O) is a pressure unit used to express measurements in this converter.
HistoryThis unit is included because it appears in practical measurement systems, technical references, product specifications, or everyday conversion needs.
Current useUse millimeter of water when comparing pressure values, checking specifications, converting between systems, or preparing quick estimates.
| inch of water [inH2O] | millimeter of water [mmH2O] |
|---|---|
| 1 | 25.4 |
| 2 | 50.8 |
| 5 | 127 |
| 10 | 254 |
| 20 | 508 |
| 25 | 635 |
| 50 | 1270 |
| 100 | 2540 |
| 1000 | 25400 |
Use this formula: 1 inch of water [inH2O] = 25.4 millimeter of water [mmH2O] Enter your value in the calculator and the result updates instantly.
1 inch of water [inH2O] equals 25.4 millimeter of water [mmH2O].
Yes. Use the swap button in the calculator or open the related reverse conversion link when it is listed on this page.