Convert Inches of Water to Millimeters of Mercury
1 inch of water (inH₂O) equals 1.868320204 millimeters of mercury (mmHg).
1 inH₂O = 1.868320204 mmHg
Type in either box. Scientific notation works: 1.5e-3.
Converting a list? Use the bulk inch of water to millimeter of mercury converter to paste a column from Excel.
How to Convert Inch of Water to Millimeter of Mercury
- 1 inH₂O = 1.868320204 mmHg
- 1 mmHg = 0.5352401575 inH₂O
- Example: convert 15 inH₂O to mmHg: 15 inH₂O = 15 × 1.868320204 mmHg = 28.02480305 mmHg
Reference conditions. inH₂O: Conventional water column: ρ = 1000 kg/m³ and gₙ = 9.80665 m/s² (≈ water at 4 °C). mmHg: Conventional mercury column: ρ = 13 595.1 kg/m³ and gₙ = 9.80665 m/s² (≈ mercury at 0 °C / 32 °F).
Formula
mmHg = inH₂O × 1.868320203603
Derivation from SI units:
- 1 inH₂O = 1000 kg/m³ × 9.80665 m/s² × 0.0254 m = 249.08891 Pa
- 1 mmHg = 13 595.1 kg/m³ × 9.80665 m/s² × 0.001 m = 133.322387415 Pa
- 1 inH₂O = 249.08891 Pa ÷ 133.322387415 Pa per mmHg = 1.868320203603 mmHg
Both units are defined exactly, so the factor is exact. Inch of Water definition: inch of water; Millimeter of Mercury definition: millimeter of mercury.
Worked examples
- A reading of 0.3 inH₂O converts to 0.5604960611 mmHg.
0.3 inH₂O × 1.868320204 = 0.5604960611 mmHg - A value of 3 inH₂O is 5.604960611 mmHg.
3 inH₂O × 1.868320204 = 5.604960611 mmHg
Inch of Water to Millimeter of Mercury conversion table
| Inches of Water (inH₂O) | Millimeters of Mercury (mmHg) |
|---|---|
| 0.01 inH₂O | 0.01868320204 mmHg |
| 0.02 inH₂O | 0.03736640407 mmHg |
| 0.03 inH₂O | 0.05604960611 mmHg |
| 0.05 inH₂O | 0.09341601018 mmHg |
| 0.1 inH₂O | 0.1868320204 mmHg |
| 0.15 inH₂O | 0.2802480305 mmHg |
| 0.2 inH₂O | 0.3736640407 mmHg |
| 0.25 inH₂O | 0.4670800509 mmHg |
| 0.3 inH₂O | 0.5604960611 mmHg |
| 0.4 inH₂O | 0.7473280814 mmHg |
| 0.5 inH₂O | 0.9341601018 mmHg |
| 0.75 inH₂O | 1.401240153 mmHg |
| 1 inH₂O | 1.868320204 mmHg |
| 1.5 inH₂O | 2.802480305 mmHg |
| 2 inH₂O | 3.736640407 mmHg |
| 2.5 inH₂O | 4.670800509 mmHg |
| 3 inH₂O | 5.604960611 mmHg |
| 4 inH₂O | 7.473280814 mmHg |
| 5 inH₂O | 9.341601018 mmHg |
| 7 inH₂O | 13.07824143 mmHg |
| 10 inH₂O | 18.68320204 mmHg |
| 11 inH₂O | 20.55152224 mmHg |
| 14 inH₂O | 26.15648285 mmHg |
| 20 inH₂O | 37.36640407 mmHg |
| 27.7 inH₂O | 51.75246964 mmHg |
Where it's used
Inches of Water are used for HVAC total external static pressure (residential ≈ 0.5 inH₂O), while millimeters of mercury appear in blood pressure (e.g. 120/80 mmHg). Both measure pressure, stress and differential pressure (force per unit area), so the conversion is a fixed factor.
Inch of Water to other pressure units
| Conversion | 1 inH₂O equals |
|---|---|
| inch of water to pascal | 249.08891 Pa |
| inch of water to kilopascal | 0.24908891 kPa |
| inch of water to megapascal | 0.00024908891 MPa |
| inch of water to psi | 0.036127292 psi |
| inch of water to bar | 0.0024908891 bar |
| inch of water to millibar | 2.4908891 mbar |
| inch of water to decibar | 0.024908891 dbar |
| inch of water to torr | 1.86832047 Torr |
| inch of water to millimeter of mercury | 1.868320204 mmHg |
| inch of water to millimeter of water | 25.4 mmH₂O |
| inch of water to centimeter of water | 2.54 cmH₂O |
| inch of water to inch of water (60 °F) | 1.001000281 inH₂O (60 °F) |
| inch of water to inch of mercury | 0.07355591353 inHg |
| inch of water to atmosphere | 0.002458316408 atm |
| inch of water to barye | 2490.8891 Ba |
Frequently asked questions
How many millimeters of mercury are in 1 inch of water?
1 inH₂O = 1.868320204 mmHg.
How do I convert inches of water to millimeters of mercury?
Multiply the value in inH₂O by 1.868320204. For example, 15 inH₂O × 1.868320204 = 28.02480305 mmHg.
Is the inH₂O to mmHg conversion exact?
Yes. Both units are defined exactly, so the ratio is exact; its decimal form does not terminate and is shown here to 10 significant figures (more with the precision selector).
Sources
- Guide for the Use of the International System of Units (SI), NIST Special Publication 811, 2008 Edition, National Institute of Standards and Technology , Appendix B.8, "inch of water, conventional (inH2O)".
- Guide for the Use of the International System of Units (SI), NIST Special Publication 811, 2008 Edition, National Institute of Standards and Technology , Appendix B.8, "millimeter of mercury, conventional (mmHg)".
Last reviewed: . Factors are stored exactly and computed with 50-digit decimal arithmetic. See how we verify conversion factors.
Cite this page
APA
Scientific Converters. (2026, October 15). Convert Inches of Water to Millimeters of Mercury. Retrieved October 17, 2026, from https://scientificconverters.com/pressure/inch-of-water-to-millimeter-of-mercury/
IEEE
Scientific Converters, "Convert Inches of Water to Millimeters of Mercury," scientificconverters.com. Accessed: Oct. 17, 2026. [Online]. Available: https://scientificconverters.com/pressure/inch-of-water-to-millimeter-of-mercury/